An error SHOULD NOT result if some or all of the requested locales are not supported by the OpenID Connect Provider.
When the OP determines, either through the Claims_locales Parameter, or by other means, that the Resource Owner and OAuth Client are requesting Claims in only one set of languages and scripts, it is RECOMMENDED that OpenID Connect Providers return Claims without Language-Tags when they employ this language and script.
It is also RECOMMENDED that OAuth Clients be written in a manner that they can handle and utilize Claims using Language-Tags.