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Multi languages resources with proper language code

I want to make application, that will support languages with resources depending of actual localization and country code. According to Documentation I need to change resources to format i.e. values-en-rUS, and in that configuration app sucessful compile and proper flag image in resources is set it up but I dont know what format should be write in Locale variable to change resources. I try en_US , en-rUS , en-US but does doesnt work correctly. In my previous version with resources like values-en changing Locale of the app language to en the resources are updating correctly.

Locale for values-en-rUS can be obtained by new Locale("en", "US"), this will get instance of "en_US" locale (matching values-en-rUS).
Don't use new Locale("en_US") this will produce "en_us". That doesn't match values-en-rUS. Also new Locale("en-US") will not work.
From API level 21, there's handy Locale.forLanguageTag(String) method. It returns a locale for the specified IETF BCP 47 language tag string, which is "en-US" in this case. So you can use Locale.forLanguageTag("en-US).

Not totaly sure of what you asking but if you want to add languages you need to create indeed to create the write folder but in that format : <resource type>-b+<language code>[+<country code>]
example : value-b+en+US
Then you can add the strings.xml file in each folder to what you want to display. You can find all the documentation here.

Whats the standard approach to using region specific strings?

The app I work on will be launched in the UK, US and AU. I have strings.xml in values-en-rUS , values-en-rAU and values folders. I have certain strings for ex "Zipcode" which will only be used in the US so I have added them to strings.xml in values-en-rUS. I have "Postcode" as the equivalent in AU and UK strings.xml files.
This works fine as long as the device locale is set correctly ie, English(United states) in United states. If the device is in English (Australia) and the user is using the app in United states the solution fails.
Is there a standard approach for displaying a specific string irrespective of the device locale? Any help is appreciated

I think you are using the wrong localization.
values-en-rUS you are defining resources in english (locale en) for mobiles situated in the US region.
If you use values-en_US instead it should correctly work for the locale en_US.
To better understand how the fallback between the different locales will happen consider this link:
Android doc

The correct Java SE standard usage is:
Locale: Properties file name part:
Locale("en", "US") values_en_US
Locale("en", "AUS") values_en_AUS
Locale("en", "UK") values_en_UK
Best have a Locale("en") / values_en and values too.
There are some Locale constants. A small prototype will see whether this works satisfactory.

How can I have both res/values-pt_PT and res/values-pt_BR on Android?

I keep getting an error when creating folders for internationalization. But the errors appear just for folders with the name like values-xx_XX. If I have values-xx everything is ok, but like I asked in the title I want to make 2 separate folders for the (aprox.)the same language: values-pt_PT,values-pt_BR. How can I do that without getting any errors? Note: The error is not specified anywhere, the eclipse is just marking the folder with a red cross and doesn't allow me to run the project.
Every hint is appreciated. Thank you! :)

Use the format values-xx-rXX instead of values-xx_XX. In this instance you should use values-pt-rPT and values-pt-rBR.
See http://developer.android.com/guide/topics/resources/providing-resources.html#AlternativeResources
The language is defined by a two-letter ISO 639-1 language code,
optionally followed by a two letter ISO 3166-1-alpha-2 region code
(preceded by lowercase "r").

I haven't done it myself, but after a quick search here, I found Setting region based Local in android where they suggest using the constructor as you did:
Locale locale = new Locale("ar","SA"); //(language,country)
But also, if you wish to pass it as one parameter, you'd still leverage the lowercase "r" as in the "values" folder, like this:
Locale locale = new Locale("ar-rSA");
Hope it helps :)

Android. How to use the same localizable messages for all the languages in a country?

My country (Spain) has several languages (es-ES, ca-ES, gl-ES, eu-ES). We won't add all the languages for now so we would like to use main language in Spain, i.e. Spanish (es). We would like to display the /values-es/strings.xml when the user has selected one of the other languages in the country. How can we do that?
Oh, and we would like to use English as the default language (/values/strings.xml).
It would be great to have something like /values-ES/strings.xml, but I suppose that can't be done because the first code should be the language code.
Now we are copying the /values-es/strings.xml file to the other folders (values-ca, values-gl and values-eu) but we'd like to avoid that.

I think that you should have only 2 folders with 1 strings.xml for each other:
res/values/strings.xml this resource will contains your text in English ;
res/values-es/strings.xml this resource will contains your text in Spanish .
When your app is installed on a device which is configured with the Italian language, it will use the file resource on case 1.
When your app is installed on a device which is configured with a Spanish language (and there are a lot of Spanish language out there, think about South America countries), it will use the file resource on case 2.
You can do it easily with Android Studio:
right-click on res folder
go to New > Android resource directory
a window will show you some options; pick Locale and then click on the button with those symbols "> >"
then on the Language list, pick es: Spanish and then click OK, as showed in the image below (note that by default the Specific Region Only has Any Region selected!)
By experience: I never faced up a Breton, Corsican or Provençal users claiming for a full translation of the application in their language (by default the app has English as default and French).

I would say you want to do something like this.
if (Locale.getDefault().getISO3Country().equals("ESP"))
{
Locale[] locales = Locale.getAvailableLocales();
for (Locale loc : locales)
if (loc.getISO3Language().equals("SPA"))
{
Locale.setDefault(loc);
break;
}
}
Note: I'm not sure if I got the ISO3 language and country codes right. And you'll also have to do something for the (rare?) situation that the es-ES locale is not available.

If you are trying to override Catalan with Spanish, you should probably have that in the values-ca/strings.xml file.
The way to do what you are asking is to provide the resources in the appropriate mobile country code resource folder, which takes precedence over language-region resources.
Assume that you have the following situation:
The application code calls for R.string.text_a
Two relevant resource files are available:
res/values-mcc404/strings.xml, which includes text_a in the application's default language, in this case English.
res/values-hi/strings.xml, which includes text_a in Hindi.
The application is running on a device that has the following configuration:
The SIM card is connected to a mobile network in India (MCC 404).
The language is set to Hindi (hi).
Android will load text_a from res/values-mcc404/strings.xml (in English), even if the device is configured for Hindi. That is because in the resource-selection process, Android will prefer an MCC match over a language match.
The MCC for Spain is 214.
(See Localization)

I found another tricky solution: hard links. Although it doesn't remove whole problem completely, at least it protects you from routine task of copying file across multiple directories or making equal changes in all existed files with risk of miss something.
But I must admit that there is some caveats:
1) Some IDE does not support working with hard links by-default. Intellij IDEA and Android Studio will break your hard links if you don't disable "safe write" option in settings.
2) Most version control systems also doesn't support hard links by default. Let's take git for example. It will break existing hard links after reverting or merging changes.
Currently, I'm using batch file for restoring hard links after they get broken by git.

In a general term, there should be only one strings.xml file under values folder containing the relevant data.
If we explicitly specify different values folder like values-ca,values-es, whenever there are setting changes in the android device, it will look to the particular folder and take the appropriate strings value.
If the requirement is keep uniform text means better have only values->strings.xml file alone with the required data.
But with this approach multilingual apk is not possible i.e. for other country different language is expected, there will be variations again. So wherever we need uniform language, lets go with single folder alone and wherever multilingual is preferred, we can have multiple values-es,values-ca folder like that.
Hope that helps

How about trying to set it in java, instead of using strings.xml.
As doing it programatically gives you more flexibility at run-time.
Configuration config = new Configuration(getResources().getConfiguration());
Locale locale = Locale.getDefault();
String country = locale.getCountry();
String language = locale.getLanguage();
if (country.equalsIgnoreCase("ES") && (language.equalsIgnoreCase("ca") || language.equalsIgnoreCase("gl") || language.equalsIgnoreCase("eu"))) {
locale = new Locale("es");
}
config.setLocale(locale);
And then you can simply have one /values-es/strings.xml for all the ES country languages.

Which strings to store in strings.xml?

Are there any suggestions on which strings you should store in strings.xml and which strings can be stored as String objects? For example, do I have to put a string into strings.xml, if I use it only to complete a certain action and then it can be destroyed? And what is the main reason in storing strings in xml? Thanks in advance for your answers.

Any string that will be displayed to the user should be in strings.xml. This is useful in case you ever want to support other languages for your application. If you do, you just create a new strings.xml file that language with translated values. You can learn more about it here.

One reason is multi-language support.
You should store the strings that you use in Activities - TextView, button's caption and so on.

You should put most constants in strings.xml, your app title, button names, textview contents...mostly things that wont change in your application.
Another reason for storing strings in xml is for localization. You can store different files for each different Locale or language, and Android will grab the correct file for the phone's selected Locale or language.
Here is a link to the String resource Android page, it will go more deeply into how the language support is done.

You don't store all the strings in strings.xml, but only strings constants related to user interface, the strings that you want to translate in different languages.
You can have different folder like :
values
values-fr
values-de
in each a strings.xml file with you UI messages translated in many languages.
Regards,
Stéphane