Learn Hardcore French: Ma langue maternelle est différente, donc je dois souvent traduire les mots dans ma tête. - My native language is different, so I often have to translate the words in my head.

The possessive adjective must agree with the noun, not with the person:
- ma langue (feminine singular)
- mon livre (masculine singular)
- mes langues (plural)
The adjective maternel / maternelle also agrees with langue, so it must be feminine:
- langue maternelle (feminine)
- instinct maternel (masculine noun + masculine adjective)

So the correct form is ma langue maternelle, not mon langue maternel.

Why does the adjective go after the noun in langue maternelle?

In French, most adjectives come after the noun.

langue maternelle = literally “language maternal”
This is the normal pattern: un livre intéressant, une histoire drôle, une voiture rouge.

Some common short adjectives go before the noun (like grand, petit, beau, bon, mauvais, vieux, jeune, nouveau), but maternel / maternelle is not one of those, so it stays after: langue maternelle.

What exactly does langue maternelle mean? Is it the same as “native language”?

Langue maternelle normally means native language / mother tongue: the first language you learned as a child, usually at home.

Related terms:

langue maternelle – standard and very common
langue natale – also used, a bit more literary
première langue – “first language”, used in more technical/linguistic contexts
langue d’origine – “language of origin”, can refer to heritage even if it’s no longer your strongest language

In everyday speech, langue maternelle is what people most often say for “native language”.

Why is it est différente and not just est différent?

The adjective différent / différente has to agree with the noun langue, which is feminine singular.

Masculine: un accent différent
Feminine: une langue différente

Here we have:

Ma langue maternelle est différente.
→ différente matches langue (feminine).

If the noun were plural, it would be:

Mes langues maternelles sont différentes.

Different from what? Shouldn’t it say différente de…?

In isolation, est différente is a bit incomplete, but in real context, what it’s different from is usually obvious:

Ma langue maternelle est différente (de la vôtre).
Ma langue maternelle est différente (de la langue de ce pays).

You can make it explicit:

Ma langue maternelle est différente de la tienne.
Ma langue maternelle est différente de la langue parlée ici.

But if the comparison is clear from context, French (like English) can leave out the rest.

Why is there a comma before donc, and can we move donc somewhere else?

The comma marks a pause between two clauses:

Ma langue maternelle est différente, donc je dois souvent…

You have some flexibility with donc:

Ma langue maternelle est différente, donc je dois souvent traduire… (very natural)
Ma langue maternelle est différente. Donc je dois souvent traduire… (two sentences; also fine)
Ma langue maternelle est différente, je dois donc souvent traduire… (slightly more formal/emphatic)
Donc, je dois souvent traduire… (starting with Donc, is possible in speech and informal writing)

The version in your sentence is very standard and neutral.

What is the difference between donc, alors, du coup, and parce que here?

They don’t all mean the same thing:

donc = “so / therefore” (logical consequence, fairly neutral):
- Ma langue maternelle est différente, donc je dois souvent traduire…
alors = also “so / then”, a bit more conversational, less “logical”:
- … alors je dois souvent traduire… (fine in speech)
du coup = very colloquial “so / as a result / and so”, extremely common in spoken French:
- … du coup je dois souvent traduire… (spoken, informal)
parce que = “because” (introduces the cause, not the consequence):
- Je dois souvent traduire les mots dans ma tête parce que ma langue maternelle est différente.

Your sentence uses donc because it gives the consequence of the first clause, not the reason for the second one.

Why is it je dois and not something like il faut que je?

Both are possible, but they’re slightly different structures:

je dois souvent traduire…
→ uses devoir (“I must / I have to”). It feels personal and direct.
il faut que je traduise souvent…
→ uses il faut que + subjonctif (“it is necessary that I…”). This is more impersonal/abstract and a bit heavier.

For everyday speech about your own obligation or habit, je dois is the most natural choice.

Where can souvent go? Could I say je souvent dois traduire?

Souvent (often) normally goes:

After the conjugated verb if there is only one verb:
- Je traduis souvent les mots dans ma tête.
Between the auxiliary/modal and the infinitive:
- Je dois souvent traduire les mots dans ma tête. ✅

You cannot say:

✗ je souvent dois traduire (wrong word order)

Other possible placements (with slightly different emphasis or style):

Souvent, je dois traduire les mots dans ma tête. (fronted “Often, I have to…”)
Je dois traduire souvent les mots dans ma tête. (possible, but less common; sounds a bit marked)

Why is it traduire les mots and not traduire des mots?

Both are grammatically correct, but they don’t feel exactly the same:

traduire les mots
→ “translate the words” = the specific words you’re currently hearing/reading.
It suggests: whenever I’m speaking/reading, I have to translate the words (that are in front of me).
traduire des mots
→ “translate (some) words” = more indefinite, just “some words”, not necessarily the ones in a particular situation.

In this habitual sentence, les mots feels more natural, because it refers to the concrete words of the other language in general situations.

Why is it dans ma tête and not à ma tête or en ma tête?

For “in my head” (mentally), French uses dans + possessive + tête:

dans ma tête – in my head (literally and figuratively)
Ça reste dans ma tête. – It stays in my head.

À ma tête is used in other expressions but with different meanings:

faire quelque chose à ma tête – to do something my own way

En ma tête is not used in modern French.

So traduire les mots dans ma tête is the idiomatic way to say “translate the words in my head / mentally”.

Is traduire les mots dans ma tête something native speakers would actually say?

Yes, it’s natural and understandable, but in real conversation people often shorten or vary it. Common alternatives:

Je dois souvent traduire dans ma tête. (drop les mots; it’s implied)
Je traduis souvent dans ma tête.
Je suis obligé(e) de tout traduire dans ma tête.
Je pense d’abord dans ma langue maternelle, puis je traduis.

Your original sentence is perfectly correct and idiomatic, just slightly more explicit than what people sometimes say.