Using .downcase or .upcase on strings containing umlauts does not work as expected in Ruby versions before 2.4. It leaves the umlauts unchanged:

"Über".downcase
=> "Über"

"Ärger".downcase
=> "Ärger"

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The very same applies for french accents (Thanks Guillaume!):

"Être ou ne pas être, telle est la question".downcase
=> "Être ou ne pas être, telle est la question"

Obviously, this leads to problems when comparing strings:

"Über".downcase == "über"
=> false

In Rails you can use ActiveSupports' multibyte chars Show archive.org snapshot to avoid that problem. It gives you a wrapped, correctly encoded version of your string:

"Ärger".mb_chars.downcase
#<ActiveSupport::Multibyte::Chars:0x7f60b1e58dc8 @wrapped_string="ärger">

Comparison works like expected now:

"Über".mb_chars.downcase == "über"
=> true