So the search engine has been replaced by google and the links in the search output obviously have to be adapted to point to the archive.
However, I'm missing something to adapt the url. For example, google gives me this url:
https://www.inkscapeforum.com/viewtopic.php?t=664

If I replace it by

https://alpha.inkscape.org/vectors/www.inkscapeforum.com/viewtopic.php?t=664

it doesn't work.
I see there are 2 numbering systems in the new urls (perhaps it was already like this before), e.g.:

https://alpha.inkscape.org/vectors/www.inkscapeforum.com/viewtopic89ad.html?f=5&t=35639#p111349

here we have:

viewtopic89ad
and
t=35639

it's not the same number converted to hexadecimal so is there any way to deduce it?

And in case you're wondering, doing a google search with:

site:https://alpha.inkscape.org/vectors/www.inkscapeforum.com/

doesn't return all the results.

It's not quite ready yet for searching.  I've been pushing to get it ready.  But the only person (as far as I know) who knows how to make it ready, is very busy right now.  In fact, I've been told not to contact him. 

But hopefully, once 1.0 is released, it can be fixed.

It's ok that it's not ready for use, but is there really no hacky way to convert urls in the mean time? I assume the threads are all online, it only takes the right url to access them.

No, I asked Martin.  He said he had to go search the server, to find a message for me, a while back.

I just heard a rumor that instead of releasing 1.0, they're going to release 0.92.5.  That must mean that 1.0 will take much longer to release than we had hoped.

But we need to make the archive searchable.  Otherwise, it's totally useless!

Alrighty then. And yeah 1.0 is very unstable atm. I don't see it be ready soon enough.

Actually I was wrong about that.  Apparently there's some way to use a google site search to search it.  I don't know the code, but it was just posted in the chatroom, so I can copy it over here if you need it.

If there's a google advanced search that works better than the one I tried above, I would like that, but I have low hopes for it.

Put this in the google search field:

site:https://alpha.inkscape.org/vectors/www.inkscapeforum.com/ your search terms

As far as I can tell, there needs to be a space between the last / and your search terms.

That's what I wrote above and as I explained it doesn't give all the results.
No problem I'll just re-ask the questions here if I need to.

Hhmm, the person who posted that showed a video where it gives results.  Well, he'll eventually see this message, and can help you directly.

Sorry I can't be more help.

Hello,

Has somebody found a solution for the OP's problem (a way to find an old topic in inkscapeforum.com archive whith an old link like https://www.inkscapeforum.com/viewtopic.php?t=664 ?)

Thank you for listening

Maybe this in google search:

"t=664" site:alpha.inkscape.org/vectors/www.inkscapeforum.com/

Sadly , this won't work ....

what a pity that so much information is so hardly workable...

Nevertheless thank you all the same !

Worked here.

Ooops ! My apologies,

Yet I tried many times before replying !

I do realize now that when I searched from outside the forum my default search engine wasn't google... With google it works indeed.

Very happy to see this question solved.

Thank you again, Tyler.