I think you'll find that all signatories to ICAO must provide ATC services to all international flights over their territory in the English language. It is also required that all pilots who intend to operate outside their national boundaries be competent in aviation English.
Many countries use their own language when speaking to domestic airlines and pilots. This is quite legal, though it is a negative contribution to flight safety when it involves IFR traffic in the upper FIR!
It is entirely reasonable to expect a flight school offering instruction in an English-speaking country to have correct English on their promotional and instructional material, including their website. I would think twice about spending large sums of money on any service or product offered by an organisation with such poor attention to detail.
Scroggs