Même si le logiciel plante, il faut garder son calme.

Même si means even if.

• si on its own usually means if
• même si adds emphasis: even if / even though

So:

• Si le logiciel plante... = If the software crashes...
• Même si le logiciel plante... = Even if the software crashes...

In this sentence, même si introduces a concession: the crash is a problem, but the advice still stands.

Because logiciel is a masculine noun in French.

So you say:

• le logiciel = the software
• un logiciel = a piece of software / software

This is something you simply have to learn with the noun. There is no strong logic from the English word software.

Here, plante comes from the verb planter.

In everyday computing French, planter can mean:

• to crash
• to freeze
• to stop working properly

So le logiciel plante means:

• the software crashes
• the program crashes

This is a very common informal/standard way to talk about computer problems.

Be careful: une plante as a noun also means a plant, but that is unrelated here.

Because plante is the conjugated verb, not the infinitive.

The subject is le logiciel, which is third person singular, so planter becomes:

• je plante
• tu plantes
• il / elle plante

So:

• le logiciel plante = the software crashes

If you used planter, that would be the infinitive to crash / to plant, which would not fit this sentence.

Il faut is a very common impersonal expression meaning:

• it is necessary
• one must
• you have to

It comes from the verb falloir, which is mostly used only in the form il faut in the present tense.

So:

• il faut garder son calme = you have to keep calm
• more literally: it is necessary to keep one’s calm

The il here does not refer to a specific person. It is just part of the fixed impersonal structure.

Because il faut is more general and less directly aimed at one person.

Compare:

• Il faut garder son calme. = You have to keep calm / One must keep calm.
• Tu dois garder ton calme. = You have to keep calm.
  This speaks directly to one person.

So il faut is often used for:

• general advice
• instructions
• rules
• recommendations

In your sentence, it sounds like a general principle: Even if the software crashes, you should stay calm.

In French, when talking about a state or quality that belongs to the subject, French often uses a possessive adjective:

• garder son calme = literally keep one’s calm

Using le calme would sound less natural here.

Common French patterns are:

• garder son calme = keep calm / keep one’s cool
• perdre son calme = lose one’s temper / lose one’s cool

So son is the normal idiomatic choice.

No. Son here does not mean his in the sense of a specific male person.

It means one’s / your / his / her, depending on context.

In il faut garder son calme, the idea is general:

• one must keep one’s calm
• you have to keep your calm

So son agrees with the noun calme, which is masculine singular, not with the gender of a real person.

French possessives work differently from English in some cases. Here, son calme is just the standard idiom.

Yes, and it would be very natural.

Compare:

• garder son calme = keep calm / keep one’s cool
• rester calme = stay calm

Both work, but the nuance is slightly different:

• garder son calme suggests keeping control despite stress
• rester calme is a bit more straightforward: remain calm

So a natural alternative would be:

• Même si le logiciel plante, il faut rester calme.

Both are correct.

It is the present tense: plante.

French often uses the present tense in general statements and conditional-type ideas where English may also use the present:

• Même si le logiciel plante... = Even if the software crashes...

This is not a future form, even though it can refer to a possible future situation. French commonly uses the present after si and même si in this kind of sentence.

Normally, no.
Même si is generally followed by the indicative, not the subjunctive.

That is why you have:

• Même si le logiciel plante...

and not a subjunctive form.

This is useful because learners often expect anything meaning although / even if to trigger the subjunctive, but même si usually does not.

It is fairly neutral, with one slightly informal element.

• Même si = neutral
• le logiciel = neutral
• il faut garder son calme = neutral
• planter for software crashing = common and slightly informal/everyday, but very normal

So the whole sentence sounds natural in ordinary spoken or written French. It is not slangy, and it is not especially formal either.

A careful pronunciation would be roughly:

mem si luh lo-ji-syèl plant, il fo gar-day son kalm

A few useful points:

• Même sounds like mem
• si le often links smoothly in speech
• logiciel is pronounced roughly lo-ji-syèl
• plante ends with a pronounced t sound: plant
• il faut sounds like il fo
• garder has a hard g
• calme ends simply as kalm; the final e is not pronounced

A more connected spoken rhythm would be something like:

Même si l’logiciel plante, il faut garder son calme.

Not a spelling change—just a natural flow in speech.

More or less, yes:

• Même si = even if
• le logiciel = the software
• plante = crashes
• il faut = it is necessary / you have to
• garder son calme = keep one’s calm

A very literal version would be:

Even if the software crashes, it is necessary to keep one’s calm.

But the best natural English is:

Even if the software crashes, you have to keep calm.

or

Even if the software crashes, you need to stay calm.