Need filter to catch untranslated strings

[sirzooro]

Currently I am translating many WP plugins to my language. Sometimes it is a bit difficult to find correct context for translated strings, so I decided to simplify things a bit and write plugin which will append "@@" at beginning of untranslated strings. I can do this using gettext filter, but this solution has one drawback - I cannot distinguish when there is no translation from when translated text is the same as original. Therefore I am asking for new filter used for untranslated strings only, or for new param for existing one - I am not sure which will be better from performance perspective (keep in mind that many plugins are used without translations available).

Attached patch adds new filter.

New filter in wp-includes/pomo/translations.php

I don't think the potential usefulness of such a filter is worth the performance penalty.