Not update again
Are you sure that recentchanges-legend-newpage hasn't changed in English too? LocalisationUpdate only updates translations if the English text is still the same as the one used by the wiki, you may need to wait a week or so for MediaWiki to be updated there.
You need to check how it is in 1.23wmf6 on git.wikimedia.org
Well, I still don't understand what happened.
This link at line 678 retrieves the message named "recentchanges-legend-newpage." This message is defined in this link at line 1569 correctly. However, in wikipedia:th:Special:Recentchanges the recent version of "recentchanges-legend-newpage" still appears which is completely incorrect. It has been like this for almost one month.