One of my idea is to :

1. Add a DB messagesource (empty) https://www.yiiframework.com/doc/api/1.1/CDbMessageSource
2. GT do :
   1. Load current https://www.yiiframework.com/doc/api/1.1/CGettextMessageSource messagesource
   2. Load some plugin message source
   3. Load CDbMessageSource

Then : user with access to DB can update any string.

After we can construct a CDbMessageSource GUI editor

some ideas to consider:

• what will happen when a new translation is done in the core? a new entry, a changed existing translation?
• what about fallback languages so not everything needs to be copied? (swiss and austrian are identical to german in most parts, but there are differences)
• in a cascading system (like for the theme templates) individual translations can be handled easier than with one single table

having only one table/source for translations, where also individualizations are stored, no update would be possible, as you can not know which translation was from core and which from individualization.
and as long as you can not guarantee a full translation in every language you need fallbacks, which may need individualization for each language in the fallback chain.

In my idea : Core translation came from the mo files, like today, core system MUST not update DB translation. DB is used only at last, plugin can update if they really needed, but it's not in LimeSurvey API.
DB are used only for user specific translation.

Good request!

Fix committed to master branch: http://bugs.limesurvey.org/plugin.php?page=Source/view&id=33256