Im Chat schickt mir meine Sprachpartnerin die Datei, die ich sofort im Browser öffne.

Im Chat means in the chat and gives the setting first.

German often puts a time/place/context element in the first position of the sentence. When that happens, the finite verb still has to stay in second position, so you get:

Im Chat schickt ...

This is a very normal German word order pattern.

Also, im is a contraction of in dem:

• in dem Chat → im Chat

Here it is dative case because it describes a location: in the chat.

Mir is the dative form of ich.

The verb schicken often works with:

• a person who receives something = dative
• the thing being sent = accusative

So in this sentence:

• mir = to me / me (recipient, dative)
• die Datei = the file (thing sent, accusative)

So:

• meine Sprachpartnerin schickt mir die Datei = my language partner sends me the file

Meine Sprachpartnerin is the subject of the sentence, so it is in the nominative case.

A few things are happening here:

• Sprachpartnerin is a feminine noun meaning female language partner
• meine means my and matches the feminine noun
• because it is the subject, the form stays meine Sprachpartnerin

Compare:

• mein Sprachpartner = my male language partner
• meine Sprachpartnerin = my female language partner

Die Datei is the direct object, so it is in the accusative case.

With the noun Datei:

• nominative: die Datei
• accusative: die Datei

So the form looks the same in both nominative and accusative because Datei is feminine.

In this sentence, you can tell it is accusative from its role:

• the person sending = meine Sprachpartnerin
• the recipient = mir
• the thing sent = die Datei

German word order is more flexible than English, but it still follows certain rules.

The main rule here is:

• the finite verb must be in second position in a main clause

So after Im Chat takes the first position, the verb must come next:

• Im Chat schickt ...

After that, the other elements can appear in different orders. This sentence uses a very natural order:

• mir (indirect object / dative pronoun)
• meine Sprachpartnerin (subject)
• die Datei (direct object)

A native speaker might also say:

• Im Chat schickt meine Sprachpartnerin mir die Datei.

That is also correct.

German often places short pronouns like mir earlier in the sentence.

That die is a relative pronoun.

It refers back to die Datei:

• die Datei, die ich sofort im Browser öffne = the file that I open immediately in the browser

So the first die is the article:

• die Datei = the file

The second die introduces a relative clause:

• die ich sofort im Browser öffne = that I open immediately in the browser

Because it refers to Datei, which is feminine singular, the relative pronoun is die here.

Because die ich sofort im Browser öffne is a relative clause, and in German conjugated verbs go to the end of subordinate clauses.

So:

• main clause: Im Chat schickt mir meine Sprachpartnerin die Datei
• relative clause: die ich sofort im Browser öffne

Inside the relative clause:

• ich = subject
• sofort = adverb
• im Browser = location
• öffne = verb at the end

This is one of the biggest differences from English.

Because im Browser describes where the file is opened, not movement into something.

German often uses:

• dative for location: where?
• accusative for direction/movement: where to?

Here:

• im Browser = in the browser → location, so dative
• in den Browser would suggest movement into the browser, which is not the idea here

So:

• ich öffne die Datei im Browser = I open the file in the browser

Also, im = in dem, so Browser is treated as masculine here:

• in dem Browser → im Browser

Sofort means immediately or right away.

In this sentence it modifies öffne:

• die ich sofort im Browser öffne = that I open immediately in the browser

German adverbs like sofort can move around more than in English, depending on emphasis. For example:

• ..., die ich sofort im Browser öffne.
• ..., die ich im Browser sofort öffne.

The version in your sentence sounds very natural.

German often uses the present tense where English also uses the present tense, especially for actions happening now or in a vivid sequence of events.

So:

• schickt = sends / is sending
• öffne = open / am opening

Depending on context, English might translate this as:

• In the chat, my language partner sends me the file, which I immediately open in the browser. or more naturally:
• In the chat, my language partner sends me the file, and I open it immediately in the browser.

German does not need a special progressive form like is sending or am opening.

Yes. Both are possible in English.

German relative pronouns do not map perfectly onto English which/that. In this sentence:

• die Datei, die ich sofort im Browser öffne

can be translated as:

• the file that I immediately open in the browser
• the file which I immediately open in the browser

In everyday English, that often sounds a bit more natural than which here, but both are correct.

Because all German nouns are capitalized.

So in this sentence:

• Chat
• Sprachpartnerin
• Datei
• Browser

are all capitalized simply because they are nouns.

This is a standard rule in German and helps learners identify nouns more easily.

Exactly.

German very often combines nouns into a single compound noun. Here:

• Sprache = language
• Partner / Partnerin = partner

Together:

• Sprachpartner = male language partner
• Sprachpartnerin = female language partner

English usually writes similar ideas as separate words, but German often turns them into one noun. This is completely normal.