Tvättmaskinen är full, men jag kommer att ha tvättat allt innan ni är här.

Yes. Tvättmaskin is a common-gender noun (en-word), and the definite singular is formed by adding -en:

• en tvättmaskin = a washing machine
• tvättmaskinen = the washing machine

Swedish often attaches the as a suffix rather than using a separate word.

Swedish uses adjectives directly after är (to be), without an article:

• Maskinen är full. = The machine is full.

No a/an is used with predicate adjectives in Swedish (similar to English: “is full,” not “is a full”).

Yes, adjectives can agree with gender/number/definiteness. Here it stays full because tvättmaskinen is common gender singular in a simple predicate position. Compare:

• Ett glas är fullt. (neuter noun → fullt)
• Maskinerna är fulla. (plural → fulla)

men means but and connects two main clauses. Each side behaves like a normal main clause with Swedish V2 word order (the finite verb comes in the second position).

• Tvättmaskinen är full, (main clause)
• men jag kommer ... (another main clause)

This is Swedish future perfect: kommer att + ha + supine. It corresponds to English will have washed.
Structure:

• kommer (att) = will / am going to (future marker)
• ha = have
• tvättat = washed (supine form)

So jag kommer att ha tvättat literally means “I will have washed.”

It can often be omitted in modern Swedish, especially in speech:

• Jag kommer att ha tvättat allt ... (very common, neutral)
• Jag kommer ha tvättat allt ... (also common, slightly more informal)

In careful writing, att is frequently included.

Because tvättat is the supine, used with har/hade/ha to form perfect tenses. tvättade is the simple past.
Compare:

• Jag tvättade allt. = I washed everything. (simple past)
• Jag har tvättat allt. = I have washed everything. (present perfect)
• Jag kommer att ha tvättat allt. = I will have washed everything. (future perfect)

allt means everything (or all of it) and is the neuter singular form used for an abstract totality.
alla is used with plural countable nouns or when referring to people/things as a plural group.
Compare:

• Jag har tvättat allt. = I have washed everything.
• Jag har tvättat alla kläder. = I have washed all the clothes.

Yes. In subordinate clauses, Swedish typically places inte and many adverbs before the verb (unlike main clauses). This sentence doesn’t include such an adverb, but you can see the pattern if you add one:

• ... innan ni är här. (no adverb to show the difference)
• ... innan ni inte är här. (rare/odd meaning, but shows placement)
• More natural example: ... innan ni faktiskt är här. (faktiskt often sits before/after depending on emphasis, but subordinate clauses generally don’t use V2 like main clauses.)

Main clause would be: Ni är här.
Subordinate clause keeps ni är together without moving the verb to “second position” for emphasis.

It can be either, depending on context:

• ni = you (plural) (the most common everyday use)
• Ni (capitalized sometimes) can be used as a formal “you,” but that’s less common in modern Swedish than using du with titles/names.

In many contexts, learners should assume ni is plural unless the situation is clearly formal.

Yes, and it changes nuance slightly:

• innan ni är här = before you are here (focus on being present)
• innan ni kommer = before you come (focus on the act of coming)
• innan ni anländer = before you arrive (more precise/formal)

All are grammatical; är här is very natural and conversational.