As of 03/2017: Translation disambiguation handling is now fully opened again (was decided months ago already actually, just forgot about that task...)
So translators may provide below in comments their issues with precise description (where/what [in UI and PO messages], and what are the different meanings behind same English word that are the problem).
Solution (or not :/ ) will then be decided on a case by case basis (using an existing i18n context, adding new ones, or simply tweaking original UI message).
A lot of strings in UI are untranslatable or badly translatable because same word in English is used with different significant, and in most languages this synonyms have very different translations.
E.g. is the case of "light" (both "weight" and "lamp"), "clip" (both "video" and "cut") or "frame" (both "video part" and "border").
This result in very horrible "international" UI experience, because the result of translation can become something like (in translated UI) "set compression lamp/heavy" instead of "low/high" or "video to border" instead of "cut to border" because of use of synonyms of "light" and "clip".
So, to fix at least more crazy situations, gettext context must be added or english strings must be changed (e.g. "light" in scripts/startup/bl_ui/properties_render_layer.py:86 can be changed in "lightS", "lamps" or better "light group").
In my actual translation task also different peoples manifested same problems (with french, spanish, chinese... not secondary languages!...), but adding gettext contexts require to unfreeze this kind of changes that are freezed from march 2013... 2 years is too much!
Please support unfreezing for better user experience!