S instrumentalom je lakše kad vježbam s učiteljicom, ali mi je vokativ i dalje čudan.

Because the preposition s means with, and it requires the instrumental case.

So even when you are talking about the name of a case, that noun still has to decline normally:

• instrumental = nominative
• s instrumentalom = instrumental after s

So S instrumentalom je lakše literally has the structure With the instrumental, it is easier.

Both uses are the same preposition: s = with.

• S instrumentalom je lakše = with the instrumental, it’s easier
• vježbam s učiteljicom = I practice with the teacher

In both places, s triggers the instrumental case:

• instrumental → instrumentalom
• učiteljica → učiteljicom

So this sentence is actually a nice example of how the instrumental works in two different contexts: one abstract, one personal.

Because učiteljica is a feminine noun, and after s it has to go into the instrumental singular.

For nouns like učiteljica, the instrumental singular ending is typically -om:

• učiteljica → učiteljicom
• profesorica → profesoricom
• prijateljica → prijateljicom

So s učiteljicom means with the teacher.

Because here vokativ is the subject of the second clause, so it stays in the nominative:

• vokativ = the vocative case
• Vokativ je čudan = the vocative is strange

It is not after a preposition, so there is no reason to put it in another case.

A useful contrast:

• S vokativom je teško. = With the vocative, it’s hard.
• Vokativ je čudan. = The vocative is strange.

Mi is the dative form of ja and here it means to me.
Je is is.

So mi je čudan literally means is strange to me.

Croatian often uses this pattern:

• To mi je zanimljivo. = That is interesting to me.
• Ovo mi je teško. = This is hard for me.
• Vokativ mi je čudan. = The vocative is strange to me.

English often just says The vocative is still weird to me or I still find the vocative weird.

Because čudan agrees with vokativ, which is a masculine singular noun.

Agreement in Croatian means the adjective matches the noun in gender, number, and case:

• vokativ → masculine singular nominative
• therefore čudan → masculine singular nominative

Compare:

• instrumental je čudan
• gramatika je čudna
• pravila su čudna

So čudan is there because vokativ is masculine.

Lakše is the comparative form meaning easier, and in this kind of sentence Croatian uses an impersonal structure:

• je lakše = it is easier

There is no explicit subject like it in Croatian. English needs it, but Croatian does not.

So:

• S instrumentalom je lakše. = With the instrumental, it’s easier.

You can think of lakše here as the normal way Croatian says easier in an impersonal statement.

I dalje means still, still continuing, or even now.

So:

• vokativ i dalje čudan = the vocative is still strange

It often suggests that something was true before and continues to be true now.

Examples:

• I dalje učim hrvatski. = I’m still learning Croatian.
• To mi je i dalje teško. = That is still difficult for me.
• Vokativ mi je i dalje čudan. = The vocative still feels strange to me.

Kad and kada both mean when.

• kada is the full form
• kad is shorter and very common in everyday speech and writing

So:

• kad vježbam s učiteljicom
• kada vježbam s učiteljicom

Both are correct. Kad simply sounds a bit more natural and conversational in many contexts.

Not completely. Croatian word order is flexible, but not random.

The main thing to notice is the placement of the clitics je and mi. These short words usually go near the beginning of their clause, in second position.

That is why you get:

• S instrumentalom je lakše
• ali mi je vokativ i dalje čudan

The first phrase of the clause comes first, and the clitic cluster follows it.

Some variation is possible, for example:

• Lakše je s instrumentalom
• Vokativ mi je i dalje čudan

These are also natural, but they shift emphasis a bit.

Because Croatian uses the present tense for habitual or repeated actions, just like English does in sentences such as when I practice with my teacher.

Here it does not mean only right now. It means something like whenever I practice with my teacher or when I practice with my teacher in general.

So kad vježbam s učiteljicom describes a repeated learning situation, not necessarily one happening at this exact moment.

Here s učiteljicom is correct.

Croatian uses sa only in certain situations, mostly to make pronunciation easier, for example before some consonant clusters or words beginning with s, š, z, ž:

• sa sestrom
• sa školom
• sa mnom

But before učiteljicom, normal s is used:

• s učiteljicom

So both s instrumentalom and s učiteljicom are exactly what you would expect.

Because in Croatian, the names of grammatical cases are normally written in lowercase:

• nominativ
• genitiv
• dativ
• akuzativ
• vokativ
• lokativ
• instrumental

They are common nouns, not proper names. So unless they begin a sentence, they are not capitalized.