Jag vill inte slarva med min svenska, så jag läser varje kväll.

In a normal Swedish main clause, the finite verb usually comes in second position. Here, vill is the finite verb, so inte comes after it:

• Jag vill inte slarva... = I do not want to be careless...

This is a very common pattern:

• Jag kan inte komma. = I can’t come.
• Hon tycker inte om kaffe. = She doesn’t like coffee.

So for basic statements, Swedish often puts inte after the verb, not before it like English does.

Slarva med means something like:

• to be careless with
• to neglect
• to do something sloppily
• not to put in enough care or effort

In this sentence, Jag vill inte slarva med min svenska means the speaker does not want to neglect their Swedish or be careless about improving it.

A few examples:

• Han slarvar med jobbet. = He is careless with his work / He neglects his work.
• Hon slarvar med träningen. = She is not keeping up with her training seriously.

So slarva med is a fixed expression, and the med is important.

Because slarva normally goes with med in Swedish: slarva med något.

So you say:

• slarva med svenskan
• slarva med läxorna
• slarva med maten

It is just the natural preposition used with this verb. English learners often want to translate word-for-word, but with verbs and prepositions, it is usually best to learn the whole expression:

• slarva med = be careless with / neglect

Yes, literally it means my Swedish, but in context it usually means:

• my Swedish ability
• my Swedish studies
• my Swedish level

So it does not mean you own the Swedish language. It means your personal use or knowledge of Swedish.

This is very natural in both Swedish and English:

• My Swedish is getting better.
• Min svenska blir bättre.

In Swedish, names of languages are normally not capitalized, unlike in English.

So Swedish writes:

• svenska
• engelska
• tyska

not:

• Svenska
• Engelska
• Tyska

The only time Svenska would be capitalized is at the beginning of a sentence or in a title.

Here, så means so:

• Jag vill inte slarva med min svenska, så jag läser varje kväll.
• I don’t want to neglect my Swedish, so I read every evening.

It connects two clauses and shows a result or consequence.

Be aware that så can also mean other things in other contexts, such as:

• so
• like this / like that
• then

But in this sentence, it is the conjunction so.

Because så introduces a new clause, and Swedish normally includes the subject again:

• ..., så jag läser varje kväll.

That is just like English:

• ..., so I read every evening.

You cannot usually drop jag here in standard Swedish. The second clause needs its own subject and verb.

Läser is the present tense form of läsa:

• läsa = to read
• läser = read / am reading

So:

• jag läser = I read / I am reading

After vill, the next verb stays in the infinitive:

• Jag vill inte slarva...
• vill = want
• slarva = infinitive, because it follows vill

But in the second clause, läser is the main verb of the clause, so it must be finite and agree with the tense.

In Swedish, time expressions often do not need a preposition where English uses one.

So:

• varje kväll = every evening
• varje dag = every day
• i kväll = tonight / this evening
• på kvällen = in the evening

In your sentence, varje kväll is the natural way to say every evening.

Kväll means evening, while natt means night.

So:

• varje kväll = every evening
• varje natt = every night

In this sentence, kväll suggests a normal study routine in the evening, not late at night.

Yes, often you can, but the nuance changes slightly.

• min svenska = my Swedish, my ability/use of Swedish
• svenskan = the Swedish language / my Swedish in a more general sense, depending on context

So these are both possible in many contexts:

• Jag vill inte slarva med min svenska.
• Jag vill inte slarva med svenskan.

Min svenska feels a bit more personal and focused on your own skill. Svenskan can sound a bit more general, like my Swedish studies or the Swedish language as the thing you are working on.

Literally, läser means read. But in context, it can strongly suggest study as well, especially when talking about language learning.

So this sentence literally says:

• I read every evening

But the real sense may be:

• I study every evening
• I do some reading in Swedish every evening

Swedish often uses läsa in learning contexts where English might choose study, depending on the situation.

Yes. The sentence you have is natural, but there are other common ways to express the same idea, for example:

• Jag vill inte tappa min svenska, så jag läser varje kväll.
  = I don’t want to lose my Swedish, so I read every evening.

• Jag vill hålla igång min svenska, så jag läser varje kväll.
  = I want to keep my Swedish going/active, so I read every evening.

• Jag vill inte bli sämre på svenska, så jag läser varje kväll.
  = I don’t want to get worse at Swedish, so I read every evening.

Your original sentence is still perfectly understandable and natural, especially if you want to emphasize not being careless about your Swedish.