Add documentation for development

For now just i18n.

DEVELOPMENT.md

@@ -0,0 +1,27 @@
+Development Notes
+=================
+
+Here we connect notes and howtos for development around Terminator. Feel free to extend or submit suggestions.
+
+## Translation i18n
+
+Tooling is based on [Babel](https://babel.pocoo.org), the configuration is stored in `babel.cfg`, `setup.cfg` and
+some code in `setup.py`.
+
+The POT file [po/terminator.pot](po/terminator.pot) contains the template for all translations and should be updated
+regularly, especially when messages changed inside the source code.
+
+```
+$ python setup.py extract_messages
+```
+
+Usually catalogs are updated with external translation tools, e.g. when new translations are merged. But we can update
+the catalogs here, so translators will have it more easy to pick up their work.
+This is a custom extension in `setup.py`.
+
+```
+$ python setup.py update_catalogs
+```
+
+Compilation of catalogs into the binary form, from `*.po` to `*.mo` is done during `setup.py build`, and the files are
+installed during `setup.py install`.

TRANSLATIONS.md

@@ -1,7 +0,0 @@
-### Translating Terminator into your language
-
-Localized strings are available in po/<locale>.po.  These files are compiled
-into .mo files by running `python setup.py build`
-
-If you've added a new localized string to the source code, it needs to be
-extracted to `po/terminator.pot` by running `python setup.py extract_messages`