Phrasing with two clauses & how to say 'is'?

Question

I am attempting to phrase 'I apologise/I'm sorry if my Japanese is impolite.' I have never phrased a sentence with two clauses before.

Looking at the sentence as a whole, and using SOV, the subject is myself, the object my Japanese, and the verb 'sorry':

Watashi wa no Nihongo baai bureina gomen nasai

• However, this doesn't make any sense whatsoever!

Is it correct to structure this example by first splitting the sentence into
'I am sorry' and
'my Japanese is impolite'?

By doing so, I got this phrase:

Gomen nasai
(baai)
watashi no Nihongo is? bureina.

Is this an effective method of creating two-part sentences? Does it always work to split the sentence into 'parts'?

Also, how do you say 'is' in this context?
I think it may be 'wa', but I'm unsure.

Answer 1

In Japanese the conditional clause must come first so we need to say

If my Japanese is impolite, I am sorry

Let's look at 'if'. There are at least four different ways to make 'if'. The most suitable one here is たら (tara). This is formed by adding ら(ra) to the end of the plain past tense conjugation of the verb/copula.

私{わたし}の日本語{にほんご}が無礼{ぶれい}だったらごめんなさい。
watashi-no nihongo-wa burei dattara gomennasai.

I don't know how much grammar you know but だったら (dattara) is the conditional form of だった (datta), which is the past tense form of だ (da), which is the plain form of です (desu) (actually desu is the polite form of da, but desu is what you normally learn first), which means 'to be'. This is where the 'is' is added.

I should note that I'm not a native speaker and I'm not sure if 無礼 (burei) is the natural word to use in this context.

I notice you wrote bureina. burei is a kind of word called a na-adjective (among other names) and the 'na' is only added when the word is used to directly modify a noun (e.g. bureina hito, rude person).

Regarding your understanding of は and です please see my comment on your answer here.