Small Capitals with Turkish language does not work

[sicakzibillik]

If I load babel package, the small caps (smcp) feature does not activate for Turkish, even though the font I am using supports Turkish and the Turkish letter 'i' is supported in the small caps lookup table of the font. I can reproduce this problem in PdftTx, XeLaTex and LuaLaTex.

\RequirePackage{latexbug}
\documentclass[turkish]{article}
\usepackage[turkish, provide=*]{babel}
\begin{document}
Small capitals form of i with Turkish language: \textsc{i}
\end{document}

[jbezos]

Have a look at https://tex.stackexchange.com/questions/573087/print-out-all-turkish-letters-with-textsc-correctly.

[jbezos]

With many fonts, but not all, you can get the dotted i with the help of a babel transform. Requires lualatex. So, if you want to stick to a CM-like font (here {0307} is the COMBINING DOT ABOVE):

\documentclass[turkish]{article}
\usepackage[provide=*]{babel}
\babelfont{rm}{NewComputerModern10}

\babelprehyphenation[label=scdot, fonts=rm/m/sc]{turkish}{ i }{ string = i{0307} }

\begin{document}
Small capitals form of i with Turkish language: \textsc{din}

\selectlanguage{english}

Small capitals form of i with another language: \textsc{din}

\end{document}

[sicakzibillik]

@jbezos , I had searched for the problem both on Babel issues and Stack Exchange. Since the answers I found were very old, and I had read in the Babel documentation that Turkish is supported, I assumed the problem shouldn’t exist in the current Babel package. I apologize for the trouble I’ve caused.

Is it wrong to expect Babel to use the OpenType features of the selected font when Turkish is chosen as the document language? Since I’ve only recently started using LaTeX, please forgive me if my question seems nonsense?

Thank you!

[jbezos]

@sicakzibillik

Is it wrong to expect Babel to use the OpenType features of the selected font when Turkish is chosen as the document language?

In fact babel does enable the corresponding OpenType features. Libertinus Serif recognizes them, but sadly they aren’t implemented in many fonts. The issue is in the font side, not in the babel one. There are several ways to fix it, and babel transforms is one of them. (I'll add to my todo list the possibility of providing a predefined transform for this.)

[sicakzibillik]

@jbezos, I'm using the Libertinus typeface for my document. I tried both the libertinus-otf package and local Libertinus files using \setmainfont or \newfontfamily, as well as manually enabling font features. I even tried to use \babelfont—but I used it incorrectly: \babelfont{rm}{Libertinus}. Since \latexbug complained about third-party packages, and using a font other than cm/lm is out of scope, I did not add anything in the sample test file.

Now, by using \babelfont I can enable the font's smcp open type feature.

I want to clarify something: I am not insisting that this problem was caused by Babel. I am just sharing my experience. What drove me to the conclusion of opening this issue in the Babel repository is that, by using Polyglossia, I can use \textsc without defining anything or writing any macros. And, as an unfamiliar LaTeX user, I expected the same behavior from Babel.

[jbezos]

@sicakzibillik Your feedback is welcome and I'll look into how to improve compatibility with libertinus-otf.

[sicakzibillik]

@jbezos , I’d like to help as much as I can. In fact, I looked through both the babel and polyglossia repositories to see if there was a contributor guide so I could help, but I couldn’t find one. However, just as I don’t know any programming language, I also don’t know LaTeX commands. From what I can tell, the people who write the LaTeX packages handle the documentation themselves, and to create documentation, you need to understand LaTeX commands. Maybe I could do some translation? What I really want is for babel to have a solid Turkish language support.

[jbezos]

@sicakzibillik Look in the manual for “Can I help?” 🙂. But having a page with a more detailed guide on how to help is a nice idea. I’ll prepare one.