こんな感じのエラー(production環境で)が出たら
App 46 stderr: Encoding::UndefinedConversionError - U+30A1 from UTF-8 to US-ASCII:
App 46 stderr: /var/lib/gems/1.9.1/gems/sinatra-assetpack-0.3.3/lib/sinatra/assetpack/package.rb:112:in `encode'
App 46 stderr: /var/lib/gems/1.9.1/gems/sinatra-assetpack-0.3.3/lib/sinatra/assetpack/package.rb:112:in `block in combined'
App 46 stderr: /var/lib/gems/1.9.1/gems/sinatra-assetpack-0.3.3/lib/sinatra/assetpack/package.rb:108:in `map'
App 46 stderr: /var/lib/gems/1.9.1/gems/sinatra-assetpack-0.3.3/lib/sinatra/assetpack/package.rb:108:in `combined'
App 46 stderr: /var/lib/gems/1.9.1/gems/sinatra-assetpack-0.3.3/lib/sinatra/assetpack/package.rb:94:in `minify'
App 46 stderr: /var/lib/gems/1.9.1/gems/sinatra-assetpack-0.3.3/lib/sinatra/assetpack/class_methods.rb:32:in `block (3 levels) in add_compressed_routes!'
App 46 stderr: /var/lib/gems/1.9.1/gems/tilt-1.4.1/lib/tilt.rb:127:in `fetch'
環境変数LANGにen_US.UTF-8を指定してあげればとりあえず凌げる。
Passengerの場合は設定ファイルに以下の行を追加すれば環境変数を設定できる。
passenger_set_cgi_param LANG en_US.UTF-8;