A key decider is: were the strings that you had created ever *committed* to the repository?
* If they were just local *untracked* files on your computer, and you overwrote them during a merge that happened during an "unstash" (e.g. "Update Project"), then you might be out of luck.
* But, if you these strings you want back were ever committed to the repository (even just your local repository, not GitHub), then you should be able to recover them.
(Other answers are suggesting looking on GitHub, which is fine, but that won't work if you only had committed the strings locally, and never PUSHED them.)
Inside Android Studio itself, you should be able to right click on the file that lost the data, and view previous versions (maybe under the "git" menu?) of that file. You can then copy the pieces of the file that you need back into the current version, and make a new commit with those changes.