Found this on O365 Service Health dashboard. Seems to be known issue
Title: Sharing invitation messages sent using the wrong language
User Impact: New external users may receive sharing invites from
SharePoint Online or OneDrive for Business in the wrong language.
More info: This issue is intermittent in nature, and appears to only
affect a small subset of the share invite messages that are
automatically generated when a site is shared to new external users.
Users that have received share invites previously do not appear to be
Current status: Our investigation determined that there was a recent
change in localization behavior, possibly related to an update
intended to improve localization across the service. While we continue
our analysis of the root cause, we've collected enough data to start
formulating a fix which should resolve the issue. We anticipate that
we'll be ready to start testing the fix within the next two days, and
if the results are positive, we'll then roll the fix out broadly. By
Friday, March 24, 2017, we expect to have the fix deployed broadly
enough to verify whether it resolves the underlying problem.
Scope of impact: A few customers have reported this issue, and our
analysis indicates that this issue could potentially affect any
sharing invite message sent to external users by the SharePoint Online
or OneDrive for Business services.