If your font supports Turkish and also contains OpenType features that make use of the dotted i and idotless, like small capitals and petite capitals, be sure to add localized forms for Turkish i, as there is something unusual with the Turkish alphabet. Like numerous other languages it is based on Latin script, but instead of 2 types of i, namely a lowercase i with dot and an uppercase dotless I, it contains four types. This creates an issue as the default case rules no longer apply. If you capitalize i it becomes I, but not with Turkish text, as then the i becomes İ and ı becomes I.
The regular small capitals and petite capitals features don’t take these rules into account, and will change the regular lower case i into a capital dotless I, thus fail for Turkish. In this case localized forms can be used to fix this language specific issue.
Add Localized Forms Feature for Turkish i
You can easily add the localized forms feature to your fonts with FontCreator. First ensure that you have an additional glyph named i.dotaccent which is a copy of the regular i. Your font already contains this glyph if you’ve used the tranform script named Unmapped Latin Small Capitals. If not, run the glyph tranform script, or manually add the missing glyph through the Insert Glyphs dialog. Provide this glyph formula within the By Name text area:
If your font contains petite capitals as well, add that variant too.
Next, go to the OpenType Designer and click the toolbar item in the upper left corner. Ensure that the Common Localized Forms option is checked along with other features you want, like Small Capitals and Petite Capitals, and click the OK button to generate the OpenType layout features.
The OpenType features and lookups are now added to your font as shown above. As there are several more languages (Azerbaijani, Crimean Tatar, Kazakh, and Tatar), which suffer from the same issue, those also include the same fix, so no need to worry about that.
You can type preview text to test your features. You can either type a letter or a slash followed by the glyph name of the letter. You can even add newlines and override OpenType layout feature settings as we did to show the difference between regular text and small capitals.
İzin kız iktisadî /newline/otsettings+smcp+c2sc İzin kız iktisadî
Note that Turkish also supports i circumflex, which is hardly used nowadays and won’t cause issues as the uppercase of î is Î, just like in other Latin based languages.
Your feedback, suggestions for improvements, and questions related to this and other tutorials are welcome; please post them to the High-Logic Font Forum.