fastlaneで "incompatible character encodings: US-ASCII and UTF-8" エラー

swiftの開発でfastlaneを利用しています。
fastlaneを実行すると↓のようなエラーが発生。

bundler: failed to load command: fastlane (/Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/bin/fastlane)
Encoding::CompatibilityError: [!] incompatible character encodings: US-ASCII and UTF-8
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane/lib/fastlane/fast_file.rb:20:in `tr!'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane/lib/fastlane/fast_file.rb:20:in `initialize'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane/lib/fastlane/lane_manager.rb:12:in `new'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane/lib/fastlane/lane_manager.rb:12:in `cruise_lane'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane/lib/fastlane/command_line_handler.rb:30:in `handle'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane/lib/fastlane/commands_generator.rb:104:in `block (2 levels) in run'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/commander-fastlane-4.4.5/lib/commander/command.rb:178:in `call'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/commander-fastlane-4.4.5/lib/commander/command.rb:153:in `run'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/commander-fastlane-4.4.5/lib/commander/runner.rb:476:in `run_active_command'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane_core/lib/fastlane_core/ui/fastlane_runner.rb:39:in `run!'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/commander-fastlane-4.4.5/lib/commander/delegates.rb:15:in `run!'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane/lib/fastlane/commands_generator.rb:303:in `run'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane/lib/fastlane/commands_generator.rb:42:in `start'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/fastlane/lib/fastlane/cli_tools_distributor.rb:66:in `take_off'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/gems/fastlane-2.44.1/bin/fastlane:20:in `<top (required)>'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/bin/fastlane:22:in `load'
  /Users/iosbuild/work/ra-mail/.bundle/ruby/2.4.0/bin/fastlane:22:in `<top (required)>'

エラーの内容を見て見ると、

incompatible character encodings: US-ASCII and UTF-8

とある。

$ export LANG=ja_JP.UTF-8

とLANGの設定をしてあげれば、エラーが解消。

無事にfastlaneのコマンドを実行できた。