Typing Turkish characters is not very smooth in current version with English QWERTY layout.
If it is not easy to create a Turkish QWERTY layout in a short time for the developers, I have a more easy customization offer for Turkish characters: ç, ğ, ı, ş, ö, ü . So, SwiftKey developers will not need to change English Qwerty layout radically. This may work as a quick or early solution. In summary, I say that change the order of selection of Turkish characters from second to first (for c, g, i, o, s and u) and we will be able to type them easily by just pressing these letters long. OR please provide this as an option for Turkish users.

In details:

1- These (ç, ğ, ı, ş, ö, ü) are second options; if you press long to c, g, i, o, s and u. If you press long and release these keys, Swiftkey X prints: ^, *, 8, #, 9 and 7. To type ç for example; you need to press long to c and select second option ç. Too much work for a single letter.

My idea is to change these first options to Turkish characters for c, g, i, o and u. So when we press c, it will print c. If we press long to c and release, it will print ç, we will press long to c and select ^ as the second option.

We in Turkish, definitely type ç and ş more frequently than ^ and # . It is true for ğ and *. In a Turkish text or message we use ü, ı and ö more frequently then the numbers 7 8 9.

So if possible, and if it seems reasonable to you, please change the current key selection structure of

(c - ^ - ç) (g - * - ğ), (i - 8 - ı), (s - # - ş), (o - 9 - ö), (u - 7 - ü)

to

(c - ç - ^) (g - ğ - *), (i - ı - 8), (s - ş - #), (o - ö - 9), (u - ü - 7)

in the next update. OR please provide this as an option for Turkish users.