We have a book in where the designer chose Bembo as the text font. This book has a spattering of Turkish words; both the dotted and undoted i are used. Language tags were NOT used by either author or editor.
Now an obvious design solution for this sort of text is to use a font like Sabon, where not using the fi ligature causes no problem. Set everything without fi & ffi ligatures, no need to sort between Turkish & English. But that's not how current designers think; she picked Bembo.
Bembo without ligatures doesn't really solve the problem for Turkish; the terminal of the "f" half blots out the dot on the "i". You would have to positive kern the "i" quite a bit to make the dot clear, and the resulting space would give rise to a different confusion.
For Bembo anyway, it isn't that hard to make a special fi ligature where the dot over the "i" rides a bit lower, and the terminal of the "f" doesn't swoop down quite so far. The dot on the "i" clearly shows, so we can have a "f_i.dotted" and a regular "f" and undotted i, which solves the problem nicely, visually. The only wrinkle is that with the sequence fii, the dots on the two i's wouldn't be quite the same height.
The author or editor will have to mark affected words in proof & we can make the switch.
What I wonder though, is whether or not this will appear odd to anyone who regularly reads Turkish -- will it still be seen as an error, or "unfortunate"?