Update translation doc

docs/translations.markdown

@@ -5,24 +5,72 @@ How to translate Miniflux to a new language?
 --------------------------------------------
 
 - Translations are stored inside the directory `locales`
-- There is sub-directory for each language, by example for french we have `fr_FR`, for italian `it_IT` etc...
+- There is a sub-directory for each language, by example for the French we have `fr_FR`, Italian `it_IT` etc...
 - A translation is a PHP file that return an Array with a key-value pairs
 - The key is the original text in english and the value is the translation for the corresponding language
+- **French translations are always up to date**
+- Always use the last version (branch master)
 
-French translations are always up to date (because I am french).
+### Plurals
+
+Each translation file has a plural formula defined. This formula is used to determine wether a plural for the current number is needed. For languages with multiple plurals, the formula determine which plural form is the right one.
+
+You can get the formula for your language from https://localization-guide.readthedocs.org/en/latest/l10n/pluralforms.html.
+
+The formula need to be adjusted to be valid php code. Do not hesitate to ask for an adjusted formula in the bugtracker.
+
+You need to create a list of strings for terms that have a plural. For example the plural for the English translation looks like the following:
+
+```
+    'plural' => function($n) { return ($n != 1); },
+    'After %d day' => array('After %d day', 'After %d days'),
+```
 
 ### Create a new translation:
 
 1. Make a new directory: `locales/xx_XX` by example `locales/fr_CA` for French Canadian
 2. Create a new file for the translation: `locales/xx_XX/translations.php`
-3. Use the content of the french locales and replace the values
+3. Use the content of the French locale and replace the values
 4. Inside the file `models/config.php`, add a new entry for your translation inside the function `get_languages()`
 5. Check with your local installation of Miniflux if everything is ok
-6. Send a pull-request with Github
+6. Send a [pull-request with Github](https://help.github.com/articles/using-pull-requests/)
 
 How to update an existing translation?
 --------------------------------------
 
 1. Open the translation file `locales/xx_XX/translations.php`
-2. Missing translations are commented and the values are empty, just fill blank and remove comments
-3. Check with your local installation of Miniflux and send a pull-request
+2. Missing translations are commented with `//` and the values are empty, just fill blank and remove the comment
+3. Check with your local installation of Miniflux and send a [pull-request](https://help.github.com/articles/using-pull-requests/)
+
+How to add new translated text in the application?
+--------------------------------------------------
+
+Translations are displayed with the following functions in the source code:
+
+- `t()`: escaped HTML text
+- `tne()`: displayed with no escaping
+- `dt()`: date using `strftime()` formats
+
+Always use the english version in the source code.
+
+How to find missing translations in the applications?
+-----------------------------------------------------
+
+From a Unix shell run:
+
+```bash
+./scripts/find-strings.sh
+```
+
+All missing translations are displayed on the screen. Put that in the french locale and sync other locales (see below).
+
+How to synchronize translation files?
+-------------------------------------
+
+From a Unix shell run this command:
+
+```bash
+./scripts/sync-locales.php
+```
+
+The french translation is used a reference for other locales.