Question: In spoken conversations the grammar used is sometimes very different from the rules that we learn in textbooks or that apply to writing. This is even more so in regional dialects when sentences like

> 
> Das ist der Erich, dem wo seine Frau davongelaufen ist.
> 
> 
> 

are perfectly understood and spoken just like above.

How do we prepare to differentiate a regional grammar from official grammar rules when traveling to Germany?

Answer: 
I think it would help you to take a look at this question:  

[In welchen Regionen ist die dem-sein-Form gebräuchlich?](https://german.stackexchange.com/questions/48/in-welchen-regionen-ist-die-dem-sein-form-gebrauchlich) 

Avoiding bad grammar is easier when you understand how the bad grammar works.
Do not go to Switzerland. Their grammar is different from the one of Standard German.

* Future only in the combined form with "werden"
* No Präteritum, only Perfekt
* No Plusquamperfekt
* Konjuktiv 1 is hardly used
* Konjuktiv 2 is used even less, if at all
* Words and combinations that do not work in Standard German