Currently, localized versions of kmail2 don't come with localized Subject Prefixes for "Re:" and "Fwd:", such as the ones listed in http://en.wikipedia.org/wiki/List_of_email_subject_abbreviations#Abbreviations_in_other_languages.

While the use of the standard English prefixes is recommended, detecting answers and forwards with localized prefixes is important:
- to avoid piling up of prefixes in subject lines such as "Re: Aw: Re: German" or "Re: R: Re: Italian"
- to allow for correct threading.

The easier way would be just adding the localized subject prefixed for the current system language. In this case, it could even be moved to "systemsettings".
However, this wouldn't help in many use cases, as someone using KDE in English language might receive mails with e.g. a German prefix.

So probably common localized prefixes should be shipped with kmail for all languages. However, in order not to do too much filtering, only the English prefixes and the prefixes of the current system language should probably be enabled on default.

This would mean we need a more sophisticated UI for subject prefixes in the config dialog. This would however be a good idea anyway, because the current UI is incomprehensible for users that aren't proficient in regular expressions (= most users).

Reproducible: Always