How to make Arabic fonts in GIMP work

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Add it in the Language Preferred Fallback List as you did, but make sure you are using the PostScript name for the font. It has to be exact!

<array>
    <!-- for Thai  -->
    <string>th</string>
    <!-- below is the case sensitive PostScript name  -->
    <string>CSPraJad</string>
</array>

References:
https://gist.github.com/Moligaloo/3180490
https://github.com/zerustech/font-fallbacks-tutorial
https://github.com/zonble/tcfail/

In OS X El Capitan 10.11 Terminal was changed to use minimal font smoothing for light-on-dark text, which more closely matches the weight of dark-on-light text with normal smoothing intensity, and makes the text sharper and more readable, opening up counters like the hollow space in the letter “e”.

A natural consequence of this is that light-on-dark text can appear less bright than before. Users can adjust colors in Terminal’s preferences if they wish.

UI controls (NSControl) do the same, but the standard OS X text view (NSTextView) does not, so programs like TextEdit and Xcode still draw light-on-dark text with more intense font smoothing.

“…is there a way to apply this in other applications as well?”

Without some hackery to modify individual applications, they are only affected if they use standard Cocoa controls and text views.