I downloaded a keyboard-changing app, but as I used it, everything crashed, so I deleted it from my phone. Bad choice, since the app I deleted was my default keyboard. Now I have no keyboard, and I can't access the "Current keyboard" tab under Language & Input. How do i get my keyboard back?
You should sideload one from your PC and install it via adb or a file browser. You can download the Google Keyboard from here for example, and should then copy it onto your device to somewhere accessible with a file browser. You may need to enable Unknown Sources on your device before browsing to the
.apk and installing it.
If you don't have a working file browser you will need to install the SDK Tools and enable USB Debugging on your device (first enable Developer Options by tapping the build number under Settings → About seven times). Then from a shell/command prompt on your device you can run:
adb install path/to/downloadedkeyboard.apk
You can install the Google keyboard from Google Play. If the Google keyboard is already installed but broken for some reason, you can try Google Japanese Input. It comes with an English keyboard.