Learn Turkish: Tebrikleriniz için teşekkür ederim. - Thank you for your congratulations.

Auxiliary verbs like etmek and olmak are only merged into a single word with the preceding noun if a sound change occurs in that noun. This usually means a vowel drops (like sabır becoming sabretmek) or a consonant doubles (like his becoming hissetmek). Because teşekkür doesn't undergo any sound changes when paired with etmek, the two words remain separated by a space.

Does the double 'k' in teşekkür count as the consonant gemination we've been studying?

No, it doesn't. The double 'k' is simply how the root noun is spelled (it's a loanword from Arabic). The consonant gemination rule for auxiliary compounds only applies when the final consonant of a noun doubles upon meeting the vowel of the helper verb (for example, hak + etmek = hakketmek). Since teşekkür ends in 'r' and doesn't double its final letter, the gemination rule doesn't apply here.

Let's break down Tebrikleriniz—why do we need the plural suffix here?

Just like in English, "congratulations" is conventionally used in the plural form when celebrating someone. The breakdown is tebrik (congratulation) + -ler (plural) + -iniz (your, formal/plural). If you said tebrikiniz (singular), it would technically mean "your congratulation," which sounds just as unnaturally specific in Turkish as it does in English.