The situation is the same with merit, I will not go into details, but it is much easier for Russian-speaking beginners to advance in rank than beginners who speak English or any other language.
The bottom line is local board only help members earn merit easier. Without local boards, they can discuss well in English, in international boards so to be honest, in most of cases, local boards are used not because of limitations in English.
I can bet that the average quality of posts that received merit would be lower than merited English posts.
In the Croatian section for more than 3 years we have a topic where local members can report their quality posts and get merits.
You can see topic here:
https://bitcointalk.org/index.php?topic=4265795.0Submitted posts can be in both Croatian and English and I would not agree that the posts awarded with merits were of lower quality than those written in the English part of the forum.
This topic has actually helped members of the local community not to miss the quality posts of other members and that all such quality posts can be rewarded with merits.