Some wordpress php, link, language questions

I have recently start using WordPress for the very first time and i have to say it is going well. i previously made my own theme with the bootstrap 3 framework and started to implement it into wordpress.

I came across allot of things i didn’t really find a good answer for.

first of all i want my website to be multi language (Dutch & French) for that I’ve installed qTranslate that works very well. But on the other hand that also gave me the problem that i had to include my header and my footer into my html editor in WordPress because the text there has to be multi language, where normally just the content is placed. Anyone else is experiencing that problem or maybe know a walk around for this?

My website contains allot of PHP because there is a payment system that is implemented into it, so i constantly need a connection to my database (MYSQL) and also am working with sessions. I’m not so far yet, tomorrow i will but can i just implement my PHP code into the well known tags <?php ?> and place them into the html editor in WordPress?

So like you already know i had to put my header into the html editor in WordPress but now i am facing a problem linking to my home page. If, in my navigation menu, i want to link to home i cannot use for example : <?php echo home_url(); ?> and i f i just use it also doesn’t work…

Appreciate for the help!