Add Load multilingual function

[fairycn]

Add the function of loading multiple languages

#7
At present, it is necessary to download the required Language file *.qm (published) or the unpublished language file *.ts before the program runs, translate and publish it, rename it to PELanguage.qm and copy it into the language directory before it can be used.

example

• file directory
  
• Use examples
  

[hasherezade]

Hi @fairycn !
Thank you for your contribution.
There are some fixes required before I can merge it.
First of all, the QApplication is initialized twice, which is a mistake, and on Linux, it causes the window to nor render at all.
Second, the mime types, and the CSS code should not be in tagged for translation.
I prepared a patch file that you can apply. You can download it from here:

https://gist.github.com/hasherezade/b8abf31d46328c16669a2a457602fb29

And then apply with the help of git:

git apply patch1.diff

Then let me know and I will merge it.

[hasherezade]

@fairycn - I see that you removed QTranslator by mistake.
This line:

QTranslator translator;

before:

	if (translator.load("Language\\PELanguage.qm")) {
		app.installTranslator(&translator); 
	}

This wasn't in the patch file. Please add the translator, and I will check again.

[hasherezade]

Looks good now, thank you!