Ĉiufoje, kiam mi surprovas la jakon, la maniko ŝajnas loza.

Ĉiufoje means every time.

It is made from:

• ĉiu = every, each
• foje = time, occasion, instance

So literally it is something like on every occasion.

You may also see it written as ĉiu fojo in other contexts, but ĉiufoje is a very common adverbial form meaning every time.

The comma separates the main idea from the kiam clause:

• Ĉiufoje = every time
• kiam mi surprovas la jakon = when I try on the jacket

So the sentence is structured like:

• Every time, when I try on the jacket, ...

In natural English we usually say Every time I try on the jacket..., but Esperanto often uses clear punctuation around inserted subordinate clauses.

Kiam means when.

Here it introduces a time clause:

• kiam mi surprovas la jakon = when I try on the jacket

So ĉiufoje, kiam... means every time when..., or more naturally in English, every time that...

Surprovas means tries on.

It comes from:

• provi = to try, test
• sur- = on

So surprovi literally suggests to try something on by putting it on the body.

This is a very common Esperanto way of building vocabulary: a prefix plus a basic root.

Because surprovi is more specific.

• provi can mean to try or to test
• surprovi means to try on clothing

So:

• Mi provas la ideon = I’m testing the idea
• Mi surprovas la jakon = I’m trying on the jacket

For clothing, surprovi makes the meaning especially clear.

Because la jakon is the direct object of surprovas.

• mi surprovas la jakon = I try on the jacket

In Esperanto, direct objects take -n.

So:

• la jako = the jacket
• la jakon = the jacket as the thing being tried on

Yes, but the sentence is talking about the sleeve in a general or context-specific way.

Esperanto often uses the singular when one relevant part is being discussed. In English we might also say:

• The sleeve seems loose even though the jacket has two sleeves.

Depending on context, this could mean:

• one sleeve in particular, or
• the sleeve area in general

So the singular is perfectly natural.

Because it refers to a specific sleeve: the sleeve of the jacket already mentioned.

Once the jacket is identified, its parts are also understood as specific. So:

• la jakon = the jacket
• la maniko = the sleeve (of that jacket)

This is similar to English:

• I put on the jacket, but the sleeve is loose.

Because loza describes the sleeve, not the manner of seeming.

• la maniko = the sleeve
• loza = loose

So la maniko ŝajnas loza means:

• the sleeve seems loose

After verbs like esti and ŝajni, Esperanto uses an adjective to describe the subject.

Compare:

• La jako estas nova. = The jacket is new.
• La maniko ŝajnas loza. = The sleeve seems loose.

If you used loze, that would be an adverb, meaning something like loosely, which would not fit here.

Yes, very much.

Ŝajni is used to say how something appears:

• ŝajnas loza = seems loose
• ŝajnas bona = seems good
• ŝajnas stranga = seems strange

It is often followed by:

• an adjective: ŝajnas granda
• a noun phrase: ŝajnas problemo
• or a clause: ŝajnas, ke...

In this sentence, it works just like English seems.

Because loza is the normal adjective for loose, not tight.

So:

• la maniko estas loza = the sleeve is loose
• la pantalono estas tro loza = the trousers are too loose

It is simply describing the fit.

Sometimes, but the meaning is slightly different.

• ĉiufoje = every time, on each occasion
• ĉiam = always

In this sentence, ĉiufoje is better because it emphasizes repeated occasions:

• Every time I try on the jacket...

If you said ĉiam, it would mean:

• Whenever I try on the jacket, the sleeve always seems loose which is understandable, but a bit less precise stylistically.

No, Esperanto word order is fairly flexible, though some orders sound more natural than others.

This sentence is very natural:

• Ĉiufoje, kiam mi surprovas la jakon, la maniko ŝajnas loza.

But you could also say:

• La maniko ŝajnas loza ĉiufoje, kiam mi surprovas la jakon.

The original version puts the time condition first, which is a common and clear choice.

Normally, no. Surprovi is treated as one verb.

Esperanto often creates new verbs by attaching prefixes directly:

• veni = come
• reveni = come back
• provi = try
• surprovi = try on

So writing sur provi would usually not be correct here.

Both are in the present tense:

• surprovas = try on / am trying on
• ŝajnas = seems

The present tense is used because the sentence describes a repeated general situation:

• whenever this happens, that is what seems to be the case

English often does the same:

• Every time I try on the jacket, the sleeve seems loose.

So this is not about one single past event, but a recurring experience.

Maniko means sleeve generally, including the sleeve of a jacket.

So:

• ĉemiza maniko = shirt sleeve
• jaka maniko = jacket sleeve

In your sentence, because la jakon is already mentioned, la maniko is naturally understood as the jacket’s sleeve.