Custom entries in lang files

I'm adding my own entries in lang-en.php but when adding/removing modules all my entries are gone. Is there a way to save them somehow in order to automatically generated with the rest every time the file changes?

Any help on this one...?

I would suggest using the Admin Panel > Settings> Language Settings

From there you can search the language key you want to overwrite, edit it, then save it. Since the default language file is 'recompiled' after module installs, I would not recommend editing the actual lang_en.php file.