TYPO3 Core

When using fe_login (or the older newloginbox) in combination with turkish, a lot of special characters are displayed as question marks (?, ?, ?).

When entered in normal content elements they work fine.

(This is my first bug report, if you need any additional information please state so =) )

TYPO3 4.2.6
TS Setup:
[globalVar = GP:L = 7]
config.sys_language_uid = 7
config.language = tr
config.locale_all = tr_TR.UTF8
config.sys_language_mode = strict
config.sys_language_overlay = hideNonTranslated
[global]

tr_TR.UTF8 only works due to a change to the TYPO3 core on my system. Alternatively en_EN.UTF8 can be used.
(issue imported from #M11151)