According to LCRI 1.7B2, give a language note when:

The language or languages of the item are not apparent from the title data text in French and English; title in English only. Example:

When the title appears in more than one language but the text is only in one language. Example:

When one or more languages cannot be transliterated or otherwise represented in the record because the language expertise is not available. Example:

When summaries are given in languages different from that of the text. Example:

See also:

13.6. Language notes (field 546)