Add a language switcher to problems

[ss0201]

For readability, add a language switcher in the problem page.

Actually I tried to do this like the image below, but since markdown is not parsed in block tags, it was not possible.

[ss0201]

It is desirable to make it possible to separate the description into 1. Japanese, 2. English, and 3. Common to Both. e.g., the image above contains Japanese descriptions (Problem Statement, Input, and Output), English descriptions (same as Japanese), and a description Common to Both (Sample Test Cases).