The Citizens first-team squad is made up of 11 different nationalities, with a high number of Spanish and Portuguese speakers.
Alongside the language rule, Guardiola also demands that his players dine together after games, according to Otamendi.
The Argentina international told Fox Sports Radio: "After games, it is obligatory to eat at the club. Diet and rest is very important as we have a very intense calendar.
"Pep is demanding about food and also that we study English, as every meeting is in that language. In December I even have an exam!
"Pep has everything in hand so that when the game comes around, everything flows well. It's all designed for the team to function perfectly. Nothing is left to chance."