Learn Romanian: Miercuri învăț engleza. - On Wednesday I learn English.

In Romanian, you don't need a preposition like 'on' before a day of the week to say that something happens on that day. Just saying Miercuri means 'On Wednesday'.

Are days of the week usually capitalized in Romanian?

No, they are written in lowercase. Miercuri is only capitalized here because it is the first word of the sentence. If it were in the middle of the sentence, it would be written as miercuri.

Where is the word for 'I' in this sentence?

The verb învăț already specifically means 'I learn'. Because the verb form tells us who is doing the action, Romanian often leaves out the pronoun eu (I).

Why does engleza end with an -a instead of an -ă?

The letter -a at the end is the definite article, meaning 'the'. In Romanian, when you talk about learning or speaking a language, you usually add 'the' to it. So, you are literally saying 'I learn the English'. The base word for the language is engleză, and adding 'the' turns it into engleza.