How many words do I know?
When I started on here, learning Portuguese about 4 years back, I'm sure there was a way to view all the words you had learnt....but I can't find it now.
Is it available for Vietnamese?
I just want to know when I'm over 1000 words....I remember reading some quote that said most people only use around 1000 words in their day to day speech...and I know it's silly, but I'll feel good when I can use 1000 Vietnamese words.
This comment is more addressed about the "day to day speech" portion of your post and is more an FYI than anything. I'm sure 1000 words is a fine benchmark to set, though I suspect you might hit it sooner than you think.
A toddler has a vocabulary base several times that size, so I imagine any conversation with 1000 words or less will be rudimentary to the point of incomprehensibility. Look at it this way; you used somewhere around 65+ unique words in this single post today, which is 6.5% of your daily allotment. I think a 5000 word vocabulary would put one more in the realm of daily speech (this will vary depending on your pacing and topics of conversation).
This isn't all bad news. You can pick up vocabulary fairly quick, and the most common words will be the ones you remember easiest due to frequency of use. Also, you probably can get by with 1000 words; you will just be constrained in what you can say.
The Words function ís, sadly, only for the original languages, but there are ways to tamper...
As an update, I am making a course on memrise by carrying over vocabulary as I progress. This might provide an indirect measure of words learned for you. I include some words that are in the grammar notes and not in the lessons, and there are some words that I collapsed or expanded on synonyms, so it might not match up exactly with the learned words.
Here is the memrise course.
As a benchmark, I have 609 words entered as of lesson 36 (Verbs 2.5).