How to translate “this”, used for an unknown thing when mentioned the first time?

Question

The word this has a couple of meanings in English. Wiktionary states 5.
I am specifically interested in the translation of the fourth meaning:

A known (thing) (used in first mentioning a person or thing that the speaker does not think is known to the audience). Compare with “a certain …”

I met this woman the other day who’s allergic to wheat. I didn’t even know that was possible!

There’s just this nervous mannerism that Bob has with his hands, and it drives me crazy.

This description led me to certain, which translates to bestimmt. Is it safe to say, that “Ich traf diese bestimmte Frau” means “I met this woman”? I am worried it does not.

I actually need this because I don’t know how to say the following:

In my country there is this tradition …

In meinem Heimatland gibt es diese bestimmte Tradition …

Is this correct?

Answer 1

I can think of three possibilities: diese eine (this single one), jene (that) and — as mentioned in a comment — (so) eine (~such a).

Take the first one if you think that the thing you refer to is unknown and possibly quite unique.

Und dann traf ich diese eine Frau, die allergisch auf Weizen reagiert. Ich wusste gar nicht, dass es sowas gibt.

Take the second one if you talk about something/someone where you think that everyone can think of something/someone else they know and have a vivid idea in their mind.

Bob hat jene nervöse Eigenart mit den Händen rumzufuchteln, die einen einfach in den Wahnsinn treibt.

Take the third one if you talk about something/someone where it’s possibly unknown but not necessarily unique.

In meinem Heimatland gibt es (so) eine Tradition, …

Answer 2

No need to make things so complicated. German has exactly the same paradoxical use of this/diese, so literal translations will do. The only thing that’s tricky is translating “there’s just” in the third sentence, but this has nothing to do with the demonstratives involved:

Ich traf neulich diese Frau, die allergisch gegen Weizen ist. Ich wusste nicht einmal, dass das möglich ist!

Bob hat einfach diese nervöse Angewohnheit mit seinen Händen, und das macht mich wahnsinnig.

In meinem Land gibt es diese Tradition, … [better: bei mir zu Hause, in meiner Heimat, in meinem Heimatland]

I have consciously let pass a few opportunities to make the translation better by using differently constructed German idioms, but again this has nothing to do with this particular use of demonstratives.

Answer 3

You could use

Ich hab neulich diese Frau getroffen (weitere Erklärung).

For example:

Ich habe neulich diese Frau getroffen, von der ich Dir schon erzählt habe.

or

Ich habe gerade diese Frau gesehen, die ich mich nicht traue, anzusprechen.

Or for your second phrase:

Wir haben da diese Tradition (weitere Erklärung).

For example:

Wir haben da diese Tradition, dass man jemanden, der unter einem Mistelzweig steht, küssen muss.