Add documentation about translation

README.md

@@ -29,8 +29,10 @@ Please refer to the provided [update instructions](UPDATE.md).
 
 - [Project Concepts](docs/Concepts.md)
 - [Directory Protocol](docs/Protocol.md)
+- [Translation](docs/Translation.md)
 
 ## Special thanks
 
 - [Beanow](https://github.com/Beanow) for his efforts to spearhead the previous version of the Friendica Directory software.
 - [Scott Arciszewski](https://github.com/paragonie-scott) for his inspiration to use Slim and his invaluable Slim app example.
+- [Saša Stamenković](https://github.com/umpirsky) for his useful list packages like [umpirsky/language-list](https://github.com/umpirsky/language-list).

docs/Translation.md

@@ -0,0 +1,62 @@
+# Friendica Directory Localization
+
+## Overview
+
+The Friendica Directory interface is available in multiple languages.
+
+We are using a gettext-like process to generate and parse translations files, which enables translators to use their usual software to translate strings.
+
+The translations files are located in `src/lang/<locale>/LC_MESSAGES/`:
+- The compiled MO file can be generated from a translation software and will be loaded by default.
+- The PO file is the main translation interface and can be loaded if the MO file doesn't exist.
+
+## Main scenarios
+
+### Add a new locale
+
+Adding a new locale requires to edit `src/settings.php` to add it to the `$settings['i18n']['locales']` array.
+
+The base translation file can then be generated with `bin/console extract-string <locale>`.
+
+### Translate existing strings
+
+PO files can be edited with translation software like [Poedit](https://poedit.net).
+Please make sure your software is able to compile MO files to update the existing one.
+
+Both PO and MO files should be committed with Git before being submitted in a GitHub pull request.
+Please refer to the [GitHub flow documentation](https://help.github.com/articles/github-flow/) if you're unfamiliar with it.
+
+### Add new translation strings
+
+Once templates/controllers files have been edited with new translation strings, you can run `bin/console extract-strings --all` to update the PO files of all available languages at once.
+
+## Translation functions usage
+
+### In templates
+
+Basic usage:
+- `$this->__('Label')` => `Label`
+- `$this->__('Label %s', 'test')` => `Label test`
+
+With context, if a base english term can have multiple meanings:  
+- `$this->p__('noun', 'Search')` => `Recherche`
+- `$this->p__('verb', 'Search')` => `Rechercher`
+- `$this->p__('noun', 'Search %s', 'test')` => `Recherche test`
+- `$this->p__('verb', 'Search %s', 'test')` => `Rechercher test`
+
+With plurals:
+- `$this->p__('Label', 'Labels', 1)` => `Label`
+- `$this->p__('Label', 'Labels', 3)` => `Labels`
+- `$this->p__('%d Label', '%d Labels', 1)` => `1 Label`
+- `$this->p__('%d Label', '%d Labels', 3)` => `3 Labels`
+- `$this->p__('%d Label', 'Labels %2%s %3%s', 1, 'test', 'test2')` => `Label test test2`
+- `$this->p__('%d Label', 'Labels %2%s %3%s', 3, 'test', 'test2')` => `Labels test test2`
+
+### In classes
+
+You will need to add the `l10n` dependency to your class before you can use it (see [Pager](src/classes/Content/Pager.php)).
+
+- `$this->l10n->gettext('Label')`
+- `$this->l10n->pgettext('context', 'Label')`
+- `$this->l10n->ngettext('Label', 'Labels', 3)`
+- `$this->l10n->npgettext('context', 'Label', 'Labels', 3)`