How i can add a new line in my code here?
There are two options (simplified code example):


$description = t('Foo.&lt;br&gt;Bar.'); (recommended)
$description = t('Foo.') . '&lt;br&gt;' . t('Bar.');


The &lt;br&gt; tag causes a line break in HTML. Both options give the same result technically. The difference is in what translators can do with it.

Option 1 treats the sentence as a unity and gives translators more flexibility. For instance, if the French translation needs to change the word order ('Barre.&lt;br&gt;Fou.'), that's possible. However the French translator would also have the possibility to leave out the line break completely.

Option 2 is more rigid. A translator could never control which part comes before the line break and which part comes after. The translator may not even know that the sentences "Foo." and "Bar." will be combined into a single page element, because they show up as separate strings in the translation interface.