TYPO3 Core

Did you try translating it via locallang.xlf files and then referencing the labels?
That's how it is intended to be used.
Apart from that I have to admit that I don't know how to handle this issue because neither does this ticket nor the one over at Claus' tracker explain which subcomponent is meant here.
Are we talking about TSConfig?

Small update - the labels can indeed be translated by using LLL references. The problem in this specific use case is that we sanitize the string used for group name and use that as part of the pageTSconfig piece that gets generated. The sanitizing routine would strip off anything considered invalid key names for pageTSconfig, causing an unexpected entry to be generated when there were nothing but invalid characters in the string that got sanitized.

So you could say there are two "problems" here:

The one immediately at hand which can be worked around using LLL references (which causes fluidcontent to generate good pageTSconfig). That one can be considered solved.

And then what should probably be considered a feature request: support for UTF-8 in key names in pageTSconfig / TypoScript.

As an example, consider the following pageTSconfig or TypoScript:

some.index.Основное = value

Currently this does not seem to compile as valid pageTSconfig - and that's the second "problem" which I would rather call a feature request: being able to use UTF-8 as key names in pageTSconfig / TypoScript. It's not a small ask, I know, but it would perhaps be useful to some users and may not be as hard to implement as it sounds (depending on how many places perform validation/regexps on keys and whether or not those use a common validation method).

Hope that makes sense! I've re-categorised and renamed (put in TypoScript category since we don't have a TSconfig specific one).

Hey,

I thought about this for a while - and decided that we won't do that. Mainly because of this:

When using cyrillic keys in TypoScript, one would need to reference them in PHP and Fluid as well. This would result into code that is built around non-english symbols, which would be a massive change and hardly maintaineable. We as TYPO3 Core propose and recommend to only write english-based PHP code. This dates back to the sheer impossible job of making the whole PHP language "UTF-8" based (which was the aim for PHP6 but was never finished as it was impossible to do).

The amount of work outweighs the benefits of having such a thing.