I think(?) in most circumstances there is some form of caveat allowing for deviation from standard phraseology to plain language when communication difficulty is experienced. Of course, if the comms problem is due to limited understanding of the language - then that might not help?
If you think differences between ICAO standard and CAP413 are hard to handle - spare a thought for the UK Mil ATCO who, according to JSP552, is required to use "civilian" phraseology when speaking to civilian pilots - This ludricous regulation (probably inserted as a sop to justify the Mil differences in the first place?) - is funnily enough given a stiff ignoring most of the time.... but one wonders what the BOIs view would be?