Encoding issue with apostrophe in query string parameter, yaml and i18n

Question

I have a parameter with an apostrophe in the query string, escaped:

class_name=John%27s

My script processes it, and gives it to a YAML file for i18n:

title: "How to sign up for %1's %2 messages:" # %2 == 'John%27s'

but the output is: John's

Instead of: John's

I tried to unescape the query parameters before giving it to YAML, and tried many combinations of format for the YAML, like !!escape and !!html, but it doesn't work.

What am I missing? Thanks.