How similar are Turkish and Arabic?
Would it make sense to study some Turkish as a stepping stone to learning Arabic?
From what I know they share some vocabulary but that's the only advantage you would have since both languages have completely different roots.
As a Turkish native speaker I can say no. They have common words but different structures. Turkish and other Turkic languages are Altaic languages while Arabic is Semitic language. For Arabic starting with Hebrew would be better however for Turkish you can start with Korean or Japanese maybe Finnish.
Arabic is harder than Turkish. I tried to learn Arabic one time in 2011 after partially learning Japanese for a year and I couldn't make out with the script or the sounds, and I was terrible at Japanese grammar. Even German grammar, which is a V2 language, and Arabic is a Semitic language whereas Turkish isn't. Arabic is the only Semitic language there was.
They share a lot of similar words because of the ottoman empire but they are not even in the same language tree. Both languages are also some of the hardest ones to learn for an english speaker. Turkish is a very unique language in a way that a word can get extremly long because of added suffixes, there are also no gender in turkish. There are six cases and it's a grade 4 language. Arabic is a huge language with tons of words and a complex grammar system. Arabic is a grade 5 language which makes it one of the hardest or even the hardest language to learn along with japanese and mandarin. Arabic also uses a different alphabet and has some extremely hard words to pronounce. I would not advise trying to learn both at once for obvious reasons. Turkish is indeed a cool language, sadly you won't get much use of it unless you work in Turkey.
Some shared vocabulary: (Turkish-Arabic) Oda- room Cay/shay- tea Doghru/dghre- straight Boza- ice cream Tamam- OK/alright Tayarre- Airplane (ucak is more common) Acel - Hurry
Source: Fluent in Turkish and levantine&Msa arabic