On Android the letter ə becomes a question mark

The text lives in res/values-az/strings.xml. If the file is not UTF-8, ə either fails the build or shows as ? on the phone.

You do not have to hide the letter in an escape. If the file is saved correctly, the word itself is written. If the editor cannot store the letter, you can put \u0259 in its place. That is the same letter.

• Put the file at res/values-az/strings.xml. The first line should be encoding="utf-8".
• If Notepad picked ANSI, save the file again as UTF-8 in Android Studio.
• Do not write encoding="windows-1254". That table does not carry ə.
• If the editor will not take the letter, write \u0259 inside the word. The screen still shows ə.
• If the app is already installed and the letter is ?, the text went into the package wrong. Fix the file and build again.

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="olke">Azərbaycan</string>
</resources>