Look at the Irish AA licences. They have a full page which,as I recall, includes an explanation of the system, the ICAO level of the holder, validity date, etc. As stated above, it's not rocket science.
As for the UK 'informal assessment' system, I'd have no problem with it whatsoever as common sense dictates that a native English speaker can identify whether or not another person is a FLUENT English speaker........except that it appears that examiners are ticking the Level 6 box, regardless of the actual ability of the candidate to speak English.
I make this statement with some authority as (a) I am a qualified English Language Proficiency Assessor at an accredited Test Centre and (b) I come across UK CAA issued PPL and CPL / IR holders on a very regular basis in the course of my work who are nowhere near ICAO Level 6 - some Level 5, more often Level 4 and occasionally pushing the boundaries of Level 4 where there is difficulty understanding them; however, they have been ticked off by the FE as Level 6 with no further assessment necessary.
The question is 'why?'. The vast majority are obviously not Fluent English speakers, so why are FE's informally assessing them as Level 6?
In a similar respect, I have been told personally by some foreign students that they don't undertake the assessment in their own country because they know that they may not pass even at Level 4 but they 'do know' (having been told by their mates) that they WILL be assessed as Level 6 during their Skills Test in the UK. That smacks of taking the 'p***' out of the examiners, to be honest.
So, I have no problem with the informal assessment procedure provided that it is being applied correctly, which doesn't appear to be the case