Transliterate Russian titles for URL keyword assessment

[CarolineGeven]

When using a Russian focus keyword in the slug of a post in WordPress, the assessment shows correctly the keyword is present. However, in the Russian URLs it's common to transliterate to the latin alphabet.

For example, greek language is in Russian Греческий язык, and transliterated it would be for examplegrecheskij-yazyk. There are more ways to transliterate.

We need to answer the following questions:

• Do we want to be able to detect transliterated texts? (this is also applicable for other non-Latin languages, such as Greek and Japanese)
• And if we want to be able to detect this, we need to decide in which way we want to detect this, as there are more ways to transliterate. For example, the Russian language has 33 characters, the English language 26.

Another suggestion could be that we give our Russian (or non Latin users) suggestions on how to transliterate within the insights box.

(discussed this with @nataliashitova )

[atimmer]

There is already some transliteration in place: https://github.com/Yoast/YoastSEO.js/blob/develop/src/config/transliterations.js#L241-L304. This is already used for URLs.

[atimmer]

cc @IreneStr