Internationalize UI text w/ german as first second lang

Adds rust-i18n and refactors all of the text copy in the app to use the
translation function so that the UI language can be dynamically updated
in the settings.

Cargo.toml

@@ -20,9 +20,12 @@ anyhow = "1.0"
 thiserror = "2.0"
 reqwest = { version = "0.12", features = ["blocking"], optional = true }
 icu_normalizer = { version = "2.1", default-features = false, features = ["compiled_data"] }
+rust-i18n = "3"
 
 [dev-dependencies]
 tempfile = "3"
+serde_yaml = "0.9"
+regex = "1"
 criterion = { version = "0.5", features = ["html_reports"] }
 
 [[bench]]