It has nothing to do with law, but with respect toward the host country to research and follow the rules… the same holds true for Americans at home or abroad…
The Flag Code requires that the US flag be flown on federal institutions, including public schools... It does not require you to fly the US flag and it does not forbid you from displaying a foreign flag….
For example, someone with Irish heritage may proudly fly an Irish flag and is not required to fly the US flag but, there was a time where hostility was shown when the German flag was flown in the US…
That prompted Theodore Roosevelt to state that we had one flag, and one language... We again are seeing the same tensions, but this time it is the Mexican flag...
The emotional tensions of the situation are understandable, but the Flag Code does not support those who want to forbid the flying of the Mexican flag within our borders without also flying the US flag...
I have my own feelings about it and won’t go into them, but you are within your rights to fly your own flag without regard to what others believe should be done, including myself…