https://example.com/foods.json?orderBy="title"&startAt="Yoğurt"&endAt="Yoğurt\uf8ff"
With the above link, I can search the data in Firebase Realtime Database Rest Api using startAt, endAt query parameters.
How can I find the results when searching with similar special characters?
For example, yoğurt and yogurt, kızartma and kizartma
I want to get the same result when written both ways.
If this is not possible with Firebase, is it possible with String methods in Javascript or Dart programming language?
There is nothing built into Firebase for performing this type of search, so you will have to do your own work to allow it.
The simplest way is to store a secondary value for each string that you want to search, where you map each character back to a single representative value you want to search on.
A very common mapping is for example to map all text to a single case (uppercase or lowercase) so that searches become case-insensitive. You can do similar for the accented characters, mapping the ğ to g. So by combining these two tricks, Yoğurt becomes yogurt.
Same for the ı you show (and İ), mapping all four I variants in the Turkish alphabet to i.
Doing this for all special characters gives you a single string value (in addition to the user input, which you should also still store) that you can use for searches.
For more on this, I recommend also reading Dan's answer here.