Using 'last, this, next' in English
Hi.
Even though I googled, it's still confusing because there're some different infomation on using last, this, and next with days of week.

Let's suppose today is Wednesday.
If I said 'last Monday', would it mean the day before yesterday or Monday in last week?

If I said 'this Monday', which day would native English speakers think first, 'this past Monday' or 'this coming Monday'?

Also in case of 'next', would 'next Saturday' mean this coming Saturday or the next one in common spoken English?

Any responses will be helpful.
Thanks in advance. :)

Question

Using 'last, this, next' in English
Hi. 
Even though I googled, it's still confusing because there're some different infomation on using last, this, and next with days of week.

Let's suppose today is Wednesday.
If I said 'last Monday', would it mean the day before yesterday or Monday in last week?

If I said 'this Monday', which day would native English speakers think first, 'this past Monday' or 'this coming Monday'?

Also in case of 'next', would 'next Saturday' mean this coming Saturday or the next one in common spoken English?

Any responses will be helpful. 
Thanks in advance. :)

Answer

I will start by saying that you may find regional variation. It might be slightly different between various Anglophone countries.

I am in the UK. For the above I would say:

1. Last Monday
The day before yesterday. It is the last Monday which has passed.

2. This Monday
This coming Monday.

3.Next Saturday
The coming Saturday is 'this Saturday'. The Saturday after that is 'next Saturday'.

Answer

I'm a native US speaker, and to me, "last", "this", and "next" can all be ambiguous when referring to days of the week. So it makes sense that it would be confusing to google the meaning, since it can definitely be different sometimes.

You can usually tell by context which day is meant. For example,
"We went to the store this Monday" vs. "We'll be going to the store this Monday".

If it's not clear by context, then you can just ask a question to clarify, such as "Do you mean Monday this week, or Monday next week?".