Re : Translating only the necessary (language related)
http://tikiwiki.org/TikiWikiInternationalizationAndLanguages
can help.
- get_strings.php with the options module can help you to see where the strings are. If you can determine which script a user can see (ex: tiki-index.php...), you can translate only the strings used in tiki-index.php or tiki-show_page.tpl or comment.tpl ... but it will not be easy.
- Perhaps you can collect the strings in lib/smarty_tiki/prefilter.tr.php and in the function tra in tiki-setup_base.php
- Look also in "using the database for the translation, there is an option about collecting untranslated strings
I don't know Turkish but is utf-8 enough?