Merge pull request #8638 from cketti/update-translations-doc

# Managing strings

We use Android's [resource system](https://developer.android.com/guide/topics/resources/localization) to localize

user-visible strings in our apps.

Our source language is English (American English to be more precise, but simply "English" (en) on Weblate).

Translations of source strings happen exclusively in our

[Weblate project](https://hosted.weblate.org/projects/tb-android/). This means the source language is only modified by

changes to this repository, i.e. via pull requests. Translations are only updated on Weblate and then merged into this

repository by the Thunderbird team. This is to avoid overlapping changes in both repositories that will lead to merge

conflicts.

## Adding a string

Add a new string to the appropriate `res/values/strings.xml` file.

Please don't add any translations for this new string to this repository. If you can also provide a translation for the

new string, wait until the change is merged into this repository and propagated to Weblate. Then translate the new

string on Weblate.

## Changing a string

Changing a string should be avoided. Weblate doesn't automatically invalidate translations when a source string is

changed. This can be worked around by removing the old string and adding a new one. Make sure to only modify the source

language. It's fine for the translations to then contain unused strings. The next merge with Weblate will remove those.

## Removing a string

Remove the source string from `res/values/strings.xml`. Don't modify translations under `res/values-<lang>/strings.xml`.

The next merge from Weblate will automatically get rid of the translated strings.

## Changing translations in this repository

This should be avoided whenever possible, as it can create merge conflicts between Weblate and this repository. If you

need to change individual strings, please translate them on Weblate instead. If a mechanical change is necessary across

all languages, this should be discussed with the core team who will use this procedure:

1. Lock all components on Weblate by clicking the "Lock" button in the

   [repository maintenance](https://hosted.weblate.org/projects/tb-android/#repository) screen.

2. Commit all outstanding changes by clicking the "Commit" button in the same screen.

3. Trigger creating a pull request containing translation updates from Weblate by clicking the "Push" button in the

   repository maintenance screen.

4. Merge that pull request containing updates from Weblate into this repository.

5. Create a pull request to change the translated files, following the established procedures to get it merged. Make

   sure you've rebased against the latest changes.

6. Wait for the changes in this repository to be automatically propagated to and processed by Weblate.

7. Unlock components on Weblate by clicking the "Unlock" button in the

   [repository maintenance](https://hosted.weblate.org/projects/tb-android/#repository) screen.

# Managing translations

Right now we're using the `resourceConfigurations` mechanism provided by the Android Gradle Plugin to limit which