let me explain.
I've joomla 1.0.12 bridged via jsmf 2.0.2 to smf 1.1.2 in wrapped mode.
joomfish 1.7 is installed.
I applied your suggested hack to the jfish selector php file.
You can reach the public forum clicking in the left menu forum item.
Now, if you're inside the forum and use the jfish country flag selector you'll see everything working: main menu (joomla's one) and all smf stuff.
If you, instead of opening the forum pages, just try to use  the country flag selector being just in the homepage, nothing will work. With the smf bridged jfish seems to fail on menus, modules, sections (of course translated in the jfish tables) IF no pages of the forum is being displayed.
You could see it direcly at lnx.musicfun.it or 69.89.31.67/~musicfun (yep, we are moving).

One more thing: the error into the log could be avoided  changing ".=" with "=" without "" of course (.= supposes to append, to concat  to a pre-existing valorized string, and $smflang was not).

Ok, sitting down waiting for ideas.
Thanks you all in advance.

Take care,
A.

Folks, I SOLVED! 

Now all is working even in wrapped mode.

The problem? A virtuemart mambot! No error logs but with tons of attempts I discovered it!

I hope this thread will avoid other users to spend time and time into a workaround.

Thanks all,

A.

I tried the hack with JoomFish Version 1.8.2 and unfortunately the homepage won't load when I apply the hack. (It stops loading when the language selector should appear).

Did anybody have success in trying the hack with newer versions of JoomFish?