Language codes : se -> sv (#6339)

* correct bengali language code

* fix language code, replace spanish links with english

* lint

* greek language code is el not gr

* language code for Korean is ko not kr

* correct swedish language code

books/free-programming-books-sv.md

@@ -0,0 +1,25 @@
+### Index
+
+* [C](#c)
+* [C++](#cpp)
+* [PHP](#php)
+
+
+### C
+
+* [C-programmering](https://sv.wikibooks.org/wiki/C-programmering) - Wikibooks
+
+
+<h3 id="cpp">C++</h3>
+
+* [Programmera spel i C++ för nybörjare](https://sv.wikibooks.org/wiki/Programmera_spel_i_C%2B%2B_f%C3%B6r_nyb%C3%B6rjare) - Wikibooks
+
+
+### MATLAB
+
+* [Introduktion till MATLAB](https://www.liber.se/plus/E470523401.pdf) (PDF)
+
+
+### PHP
+
+* [Programmera i PHP](https://sv.wikibooks.org/wiki/Programmera_i_PHP) - Wikibooks