TYPO3 Core

The default page TSconfig of the RTE contains:

RTE.classesAnchor {
    externalLink {
        class = external-link
        type = url
        titleText = LLL:EXT:rtehtmlarea/res/accessibilityicons/locallang.xlf:mail_titleText
    }
    ## ....
}

http://docs.typo3.org/typo3cms/extensions/rtehtmlarea/6.2/Configuration/PageTsconfig/classesAnchor/Index.html

If I change it to use own my own titleText values

RTE.classesAnchor.externalLink.titleText = LLL:EXT:myext/Resources/Private/Language/locallang.xlf:mail_titleText

and, of course translate the locallang.xlf in de.locallang.xlf, fr.locallang.xlf...

<trans-unit id="mail_titleText" approved="yes" xml:space="preserve">
    <source>New e-mail to me</source>
    <target>Neue E-Mail an mich</target>
</trans-unit>

The target text doesn't appear in the link wizard of the RTE but the source.

The user has German as Backend Language and creates / edit a content element on default language which is set to "de" by

RTE.default.defaultContentLanguage = de

http://docs.typo3.org/typo3cms/extensions/rtehtmlarea/6.2/Configuration/PageTsconfig/interfaceConfiguration/Index.html#defaultcontentlanguage

All other language codes are set in websitelanguage with static_info_tables.