How to memorise a word like 'thổ nhĩ kỳ'? Khó quá!
If you think about it, Thổ Nhĩ Kỳ kinda does sound like Turkey. Just broken down to three syllables =)
Sorry there is no tip in this case. Luckily, there are not many countries that names have more than three words like this in Vietnamese.
I'm not sure how to memorise it except through repetition, but at least for the select the words exercise, it starts with a T and ends with a Y like Turkey, which leaves nhĩ in the middle :)
For me best way to remember this was to listen to VOV - Việt Nam và thế giới podcast (news) on spotify.