On mnogo radi, ali i dalje uči hrvatski.

Yes. On means he, but Croatian often drops subject pronouns when the verb already shows who the subject is.

So:

• On mnogo radi, ali i dalje uči hrvatski.
• Mnogo radi, ali i dalje uči hrvatski.

Both are natural. Adding on makes the subject more explicit, and it can add a little emphasis or contrast, depending on context.

Radi is the 3rd person singular present tense of raditi (to work).

So:

• ja radim = I work
• ti radiš = you work
• on/ona/ono radi = he/she/it works

In this sentence, radi agrees with on.

Here mnogo means a lot or a great deal.

So On mnogo radi means He works a lot.

Yes, mnogo is very common. In everyday speech, you may also hear puno:

• On mnogo radi.
• On puno radi.

Both are natural, though puno is often especially common in conversation.

In Croatian, adverbs like mnogo often come before the verb they modify.

So:

• mnogo radi = works a lot

That is the most neutral word order here. Croatian word order is flexible, but this version sounds very natural and straightforward.

Ali means but.

It connects two clauses:

• On mnogo radi
• ali i dalje uči hrvatski

So it works just like English but in many cases. It normally comes at the start of the second clause after a comma, exactly as it does here.

I dalje means still, continuously, or even so / despite that, still depending on context.

In this sentence, it means something like still or continues to:

• ali i dalje uči hrvatski = but he still studies/is still learning Croatian

This expression is very common. It is made of two words, and together they function like one expression.

Yes. Još uvijek also means still.

For example:

• On mnogo radi, ali još uvijek uči hrvatski.

That is also correct and natural. The difference is small:

• i dalje often has a sense of continuing despite circumstances
• još uvijek is a very common general way to say still

In this sentence, both work well.

Uči is the 3rd person singular present tense of učiti (to learn / to study).

So:

• ja učim = I learn / I study
• ti učiš = you learn / you study
• on/ona/ono uči = he/she/it learns / studies

In Croatian, učiti can mean both to learn and to study, depending on context.

Because Croatian often uses the adjective alone to mean the language.

So:

• učim hrvatski = I’m learning Croatian
• učim hrvatski jezik = I’m learning the Croatian language

Both are correct. The shorter version, hrvatski, is very common and sounds natural.

Grammatically, hrvatski here functions as the direct object of uči.

In Croatian, names of languages are normally written with a lowercase letter.

So:

• engleski = English
• hrvatski = Croatian
• njemački = German

This is different from English. Proper names like Hrvatska (Croatia) are capitalized, but the language name hrvatski is not.

There is no hidden is, and On je radi would be wrong here.

Croatian does not use a verb like to be in the present progressive way English does. English says:

• He is working
• He is learning

Croatian simply uses the present tense:

• On radi
• On uči

These forms can mean he works, he is working, he studies, or he is studying, depending on context.

Yes, Croatian word order is flexible, but not every version sounds equally neutral.

The original:

• On mnogo radi, ali i dalje uči hrvatski.

is a very natural neutral sentence.

You might also hear variations like:

• Mnogo radi, ali i dalje uči hrvatski.
• On radi mnogo, ali i dalje uči hrvatski.

The first is very natural because the pronoun is dropped. The second is possible, but mnogo radi is usually the more neutral order.

It can be either, depending on context.

Croatian present tense often covers both:

• habitual meaning: he works a lot / he studies Croatian
• current ongoing meaning: he is working a lot / he is learning Croatian

Without extra context, the sentence most naturally sounds like a general present situation: this is what is going on in his life these days.

Because the sentence describes two simultaneous present facts:

• he works a lot
• he still learns/studies Croatian

Croatian commonly uses present tense in both clauses when both actions or states are true now. There is no need for a separate structure like English is working unless context specifically forces that interpretation in English.