Since gradle and Android studio both use UTF-8, you should consider using that. It's a good encoding too as it's based on unicode charset.
There has also been some talk on whether they should enforce UTF-8 or not in the future, so you should start changing to UTF-8 asap :)
You can change your encoding as follows below.
Click File -> Settings (or click Ctrl + Alt + S) and find File Encodings in your Androd Studio. See the image below as a reference.
Now you have three options
- change UTF-8 to match other encoding
- or change project encoding to match UTF-8 since both Gradle and
Android Lint use this (recommended)
- Ignore the warning

(source: shrani.si)
You can also see the current encoding of your file at the bottom right corner of Android studio. You can also change it there. See the image below.
