Here is an interesting anomaly in CAP 804. In section 4 Part M it states:
Whilst the EU regulations include language proficiency standards (as they are
included in ICAO Annex 1), they do not include the requirements to be complied with
to be granted a licence to operate radio communication equipment installed in an
aircraft; such licences remain under national legislation. In the UK this is a Flight
Radiotelephony Operator’s Licence (FRTOL) – See Section 6 of this CAP 804.
but in Section 6 it states:
3.2.3 Applicants for the FRTOL shall have demonstrated language proficiency in English at
Level 4, 5 or 6, which must be valid on the date that the FRTOL is issued.