Beta features have icons to represent them at Special:Preferences.
They usually show a schematic representation of a MediaWiki page with a logo in the top left corner, and this of course means that they should be flipped for RTL languages.
Some of them are trivial - just a horizontal flip.
Some of them are less trivial - for example, in the one for the VisualEditor formula editing I flipped the image and then flipped the Sigma icon inside it so it would still look like Σ and not flipped.
Some of them are even less trivial, for example the icons for the font style experiments. It shows the Latin letter A, and it's weird to show a Latin letter in the beginning of a right-to-left text. Luckily, there are only two major right-to-left scripts, so I made one icon for Hebrew and one for Arabic.
Some relevant sample commits by myself, already merged:
On this commit Jon and Juliusz complained that the image should be re-saved with a smaller size and less metadata:
The SVGs from the previous merged commits may have to be re-done as well.
Any future beta features should have RTL-compatible icons from the start, preferably done by professional designers.
See some more details here: