what is the difference between "aceasta" and "această"?
Masa aceasta (when you have a noun with definite article first), but această masă (no article). So it basically depends on the order of the words
Can't it also be: 'This meal looks heavy '?
Yes, indeed. Romanian is quite flexible, having lots of words with several different meanings. Word plays are also a common type of humour.
I wrote mare instead of pare and it didn't mark it incorrect. This is just one of probably hundreds of times I made a mistake (usually because I can't understand the speaker!) that aren't caught. Definitely need better quality control!
I think the app considers it a typo if there is only one mistaken character, at least from what I ve noticed
True, especially when the misspelled letter is near the correct one on the keyboard (not the case here, but that's the idea).