Over-reliance on English language

[flapsforty]

jensdad, in an ideal world, things would be as you describe. CC able to communicate with the pax in the pax's own language on every flight.
Most legacy airlines still put a premium on hiring cabin crew who speak more than one language, and (financially and or with making languages a requirement for promotion) stimulate their CC to speak as many languages as possible.

However, in the real world, regulations and cost-minimising are two very deciding factors,
Regulations, as in the law, used to be regarded as a minimum standard in civil aviation. Airlines used to provide a much better standard than what the law required. In most every area of the operation.
These days it is very different; many airlines view the minimum regulations regulations as the standard to strive for.

That goes for maintenance, it goes for pilot training, it goes for service standards in the cabin, for baggage handling, for the amount and quality of the food served and for most every other aspect of the business.
It is a practice commonly known among airline employees as "the race to the bottom".

Providing anything more than what the law requires adds extra costs.
Hiring people with language skills is pricier than hiring people who only speak one language. Paying your CC to add new languages or to maintain the ones they already have, costs money.
With passengers scouring the net for the cheapest tickets available, extra costs are the very LAST thing an airline is looking for.

If the pax aren´t willing to pay for it, and the law doesn´t require it, fewer and fewer airlines will be spending money on cabin crew who speak more than their native language plus English.

What does the law say?
In your example, it is a UK based airline, so we´ll limit this to European regulations.
Slightly simplified, the rules and regulations governing cabin crew are based on JAR-OPS 1.

There are no regulatory requirements regarding the minimum language skills of the individual members of the Cabin Crew. However, JAR-OPS Subpart B 1.025 “Common language” requirements does apply to all Crew members: i) an operator must ensure that all crew members can communicate in a common language and ii) an operator must ensure that all operations personnel are able to understand the language in the Operations Manual which pertain to their duties and responsibilities.

That´s it:
1) CC must have a common language
2) CC must understand their ops manual

Passengers wanting cheap seats need to realise that an airline offering those seats can and will provide nothing more than the minimum legal requirements.

Which is fair enough, since it is the only way any airline can offer those cheap seats.