"La escuela siempre es difícil."
Translation:School is always difficult.
"School always is difficult" is said in English. It has a slightly different inflection that "school is always difficult", but it is appropriate.
Here school is generalized, so the the is omitted in English. Sorry, it just sounds wrong to include it. Just as the la is required in Spanish. Both languages must be translated correctly.
It sounds really weird in english. I'm not a native speaker so I can't give you an exact answer as to why is wrong, but it sounds really really wrong.
It's a literal translation but not really a correct one because we don't say it that way in English.