Learn Hardcore Czech: Čeština je pro mě zajímavý jazyk, ale jí ještě nerozumím dobře. - Czech is an interesting language for me, but I still don't understand it well.

In Čeština je pro mě zajímavý jazyk, the real grammatical subject is čeština, but the predicate is zajímavý jazyk (interesting language).

In Czech, the adjective zajímavý must agree with the noun that it directly modifies:

jazyk is masculine inanimate (masculine noun)
therefore the adjective must be masculine: zajímavý jazyk

If you removed jazyk and said only:

Čeština je pro mě zajímavá. – Czech is interesting for me.

then you would use the feminine form zajímavá, because it would now agree directly with čeština (which is feminine).

So:

with jazyk → zajímavý jazyk
without jazyk → Čeština je zajímavá

Why is it pro mě and not pro já or pro mně?

The preposition pro (for) in Czech requires the accusative case.

The forms of já (I) relevant here are:

já – nominative (subject form: I)
mě / mne – accusative (object: me)
mně / mi – dative (to/for me) or locative (about me), depending on context

Because pro always takes the accusative:

pro + mě / mne = for me (correct)
pro + já – wrong case
pro + mně – wrong case (dative/locative, not accusative)

Colloquial, most common in speech: pro mě
More formal/literary: pro mne

So pro mě is the normal, correct everyday form here.

What is the difference between mě, mne, mi, and mně?

All of them are forms of já (I), but they differ in case and style:

mě – accusative or genitive (colloquial / neutral)
mne – accusative or genitive (more formal / literary)
mi – dative (very common in speech)
mně – dative or locative (more “full” form; often after prepositions)

Examples:

Vidí mě / mne. – He sees me. (accusative)
Nemáš mě / mne rád. – You don’t like me. (genitive/accusative)
Dej mi to. – Give it to me. (dative, colloquial)
Dej to mně. – Give it to me. (dative, stressed, often after preposition)
Mluví o mně. – He talks about me. (locative)

In your sentence, pro needs accusative, so pro mě or pro mne.

Why is it jí ještě nerozumím and not ji ještě nerozumím?

The verb rozumět (to understand) in Czech does not take the accusative (direct object) like English. It takes the dative case:

rozumět komu? čemu? = to understand whom? what? (in the dative)

The feminine singular pronoun is:

ji – accusative (direct object)
jí – dative (indirect object)

So:

Nerozumím jí. – I don’t understand her/it. (correct: dative)
Nerozumím ji. – incorrect in standard Czech

In your sentence, jí stands for češtině (dative of čeština):

ale (češtině) ještě nerozumím dobře
ale jí ještě nerozumím dobře

Both mean: but I still don’t understand it well.

Could we say češtině ještě nerozumím dobře instead of jí ještě nerozumím dobře?

Yes, and it might even be clearer for learners:

Češtině ještě nerozumím dobře.
Ještě češtině nerozumím dobře.

Both are perfectly correct and maybe more explicit than using the pronoun jí.

Your original has a pronoun to avoid repetition:

Čeština je pro mě zajímavý jazyk, ale jí ještě nerozumím dobře.
Literally: Czech is an interesting language for me, but I still don’t understand it well.

Why is it nerozumím and not something like ne rozumím?

In Czech, verbal negation is normally formed with the prefix ne- directly attached to the verb:

rozumím – I understand
nerozumím – I do not understand

You do not write the ne separately in standard present-tense negation:

ne rozumím – wrong
nerozumím – correct

This is true for most verbs:

mám → nemám – I have → I don’t have
chci → nechci – I want → I don’t want
vím → nevím – I know → I don’t know

Can the word order jí ještě nerozumím dobře be changed?

Yes. Czech word order is relatively flexible. All of these are possible and natural, with slightly different emphasis:

Jí ještě nerozumím dobře. – neutral.
Ještě jí nerozumím dobře. – slight emphasis on ještě (still).
Jí dobře ještě nerozumím. – sounds more marked; emphasis at the end.
Ještě jí dobře nerozumím. – quite natural, strong focus on dobře at the end.

In everyday speech, you’d very often hear:

Čeština je pro mě zajímavý jazyk, ale ještě jí dobře nerozumím.

Your version is also fine; it’s just one of several acceptable orders.

Why is dobře used instead of dobrý?

Dobře is an adverb, while dobrý is an adjective.

Adjective dobrý describes a noun:
- dobrý jazyk – a good language
- dobrý člověk – a good person
Adverb dobře describes how an action is done:
- mluvím dobře – I speak well
- nerozumím dobře – I don’t understand well

In jí ještě nerozumím dobře, dobře describes how you understand (well or not well), so the adverb is correct.

Why is there a comma before ale?

Ale means but and introduces a new clause that contrasts with the first one.

Czech punctuation rules require a comma before coordinating conjunctions like ale when they connect two finite clauses (each with its own verb):

Čeština je pro mě zajímavý jazyk, ale jí ještě nerozumím dobře.

Clause 1: Čeština je pro mě zajímavý jazyk.
Clause 2: Jí ještě nerozumím dobře.

So there is a comma before ale, just as in English before but in this type of sentence.

Why is Čeština capitalized?

Names of languages and nationalities in Czech are capitalized:

Čeština – Czech (language)
Angličtina – English
Němčina – German
Francouzština – French

However, adjectives of nationality are lower-case:

český jazyk – the Czech language
anglický film – an English film

So čeština (the language) is written with a capital Č at the beginning of a sentence and also normally capitalized as a proper name of the language.

Why is the verb je used? Is it always the same for he/she/it is?

Je is the 3rd person singular present of být (to be):

on je – he is
ona je – she is
ono je – it is

Czech does not usually use the pronoun when it is clear from context, so you just say:

Čeština je zajímavý jazyk. – Czech is an interesting language.

The form je is the same for he/she/it; you distinguish the gender from the noun (or an explicit pronoun), not from the verb form.

Why is jazyk used here instead of something like řeč?

Both jazyk and řeč relate to language, but they are used differently:

jazyk – language in the general, systematic sense (also tongue as a body part)
- český jazyk – the Czech language
- cizí jazyk – foreign language
řeč – more like speech, manner of speaking, or sometimes speech/language in a more abstract way
- mateřská řeč – mother tongue
- řeč těla – body language
- mít řeč – give a speech

In the standard phrase for X is an interesting language, Czech almost always uses jazyk:

Čeština je těžký jazyk.
Čeština je zajímavý jazyk.

So jazyk is the idiomatic and most natural choice here.