Belarus - everyone speaks Russian, but Belorussian is mandatory in schools
Ukraine - a vast number of people (maybe not majority but too many to be called a minority) speaks Russian as their first language but Ukrainian is mandatory in schools and all attempts to give Russian some sort of official status were meet with fierce opposition for no other reason than to preserve national identity
Tatarstan (not so sure about this one, also not a country) - Tatar is mandatory in schools for all the same reasons
Yes, all of these majority languages where once forced on the peoples of colonies by the empires. But all the people who were forced to learn them are now dead. So the current generations are forced to learn those original languages in the name of historical justice and other bullshit.
And what studies do you need for negative effects? The time learning those languages involuntarily is obviously not spent doing anything else. Is that not negative enough for you?