A question on English:

In England that could mean either interpretation.
My dad would say it and mean that he will wash the car. I would say it and mean that I'll be getting someone else to do it.
A lot depends on the area that you grew up in.
If you wanted to be more clear, then changing it to "I will" or "I'll get someone to" would do the trick.

Commonly it would mean you are having someone wash it, but you could mean you will get it done... meaning you will do it.

If you are having it done for you, say "I'm having the car washed this weekend".

If you are washing the car, say "I'm washing the care this weekend".

Saying "I will get", or "I will have" the car washed suggests someone else will do the washing.
If you will be the one doing the washing, you might say "I am going to wash the car this weekend", or "I plan to wash the car this weekend".

That implies you're getting someone else to do it.

If you said "I'll clean the car this weekend" that implies you'll do it.

@Tanaka 🤔yes you could use either interpetations if you think about it

Your get someone else to wash it. If you say I’ll wash the car it means you will do it

The word 'Get' implies someone else will do the washing. I will wash the car does not always mean you will do the washing either although it is a bit more likely that you will wash the car. What both statements are saying is that the car will be washed this weekend. Who will actually do the washing is not entirely clear.

It means someone else will do it.

“I will get.” To get. “succeed in attaining, achieving, or experiencing; obtain”

If you were doing the washing you would say “I will wash the car this weekend.”

“I will” means expressing future events.

I will get implies having others do the washing, while i will wash, implies you will do the washing

Someone else, or an automatic car wash.

My daughter will wash your car and valet inside for £10 😅

It just means it will get washed it doesn't say by who

It suggests you will bring it to a Car Wash facility.

I agree with @Ontheroad - expressed that way it could be either.

Someone else.

Someone

Someone else. Otherwise you’d say that you’ll do it.

It means neither. No one does the cleaning nor did anyone do the cleaning because to "get" the car washed means it still hasn't been washed. To "get" infers a future event and therefore has no relevance to the present moment in time, simply because the so-called 'future' as well as the 'past' do not technically exist.

Only the 'present moment' exists in reality and there are no forward or backward extensions of the present moment. Everything and anything only exists right now, this instant, which is the definition of the "present moment".

When it is said that the road to hell is paved with good intentions, this also applies to one's intent to get the car washed by any means at their disposal. This means however, that 'good intentions' can never be stated with an absolute guarantee that the task will actually be completed. That is why good intentions are not worth the breath it takes to speak them out loud.