Béarlachas is a fancy Irish word that means the use of too many English words when speaking or writing in Irish.
Let's say you speak both English and Irish, and you're trying to communicate with someone who only speaks Irish. You might use some English words accidentally, which is called béarlachas.
It's kind of like if you were playing a game of tag with your friends, but every now and then you stopped running and starting skipping instead. Skips aren't really allowed in tag, but sometimes you just do them without realizing it.
So, béarlachas is when you accidentally use English words while speaking Irish. It's not a bad thing, but it can make it harder for people who only speak Irish to understand what you're saying.