Replace hand-rolled i18n with Fluent.

Cargo.lock

@@ -799,6 +799,7 @@ dependencies = [
  "axum",
  "chrono",
  "deunicode",
+ "fluent-bundle",
  "image 0.25.10",
  "keyring",
  "liquid",
@@ -2205,6 +2206,41 @@ version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "98de4bbd547a563b716d8dfa9aad1cb19bfab00f4fa09a6a4ed21dbcf44ce9c4"
 
+[[package]]
+name = "fluent-bundle"
+version = "0.16.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "01203cb8918f5711e73891b347816d932046f95f54207710bda99beaeb423bf4"
+dependencies = [
+ "fluent-langneg",
+ "fluent-syntax",
+ "intl-memoizer",
+ "intl_pluralrules",
+ "rustc-hash 2.1.2",
+ "self_cell",
+ "smallvec",
+ "unic-langid",
+]
+
+[[package]]
+name = "fluent-langneg"
+version = "0.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7eebbe59450baee8282d71676f3bfed5689aeab00b27545e83e5f14b1195e8b0"
+dependencies = [
+ "unic-langid",
+]
+
+[[package]]
+name = "fluent-syntax"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "54f0d287c53ffd184d04d8677f590f4ac5379785529e5e08b1c8083acdd5c198"
+dependencies = [
+ "memchr",
+ "thiserror 2.0.18",
+]
+
 [[package]]
 name = "fnv"
 version = "1.0.7"
@@ -3537,6 +3573,25 @@ dependencies = [
  "syn 2.0.117",
 ]
 
+[[package]]
+name = "intl-memoizer"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "310da2e345f5eb861e7a07ee182262e94975051db9e4223e909ba90f392f163f"
+dependencies = [
+ "type-map",
+ "unic-langid",
+]
+
+[[package]]
+name = "intl_pluralrules"
+version = "7.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "078ea7b7c29a2b4df841a7f6ac8775ff6074020c6776d48491ce2268e068f972"
+dependencies = [
+ "unic-langid",
+]
+
 [[package]]
 name = "ipnet"
 version = "2.12.0"
@@ -7218,6 +7273,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c8323304221c2a851516f22236c5722a72eaa19749016521d6dff0824447d96d"
 dependencies = [
  "displaydoc",
+ "serde_core",
  "zerovec",
 ]
 
@@ -7490,6 +7546,15 @@ dependencies = [
  "toml 0.5.11",
 ]
 
+[[package]]
+name = "type-map"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb30dbbd9036155e74adad6812e9898d03ec374946234fbcebd5dfc7b9187b90"
+dependencies = [
+ "rustc-hash 2.1.2",
+]
+
 [[package]]
 name = "typed-builder"
 version = "0.23.2"
@@ -7533,6 +7598,24 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "unic-langid"
+version = "0.9.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a28ba52c9b05311f4f6e62d5d9d46f094bd6e84cb8df7b3ef952748d752a7d05"
+dependencies = [
+ "unic-langid-impl",
+]
+
+[[package]]
+name = "unic-langid-impl"
+version = "0.9.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dce1bf08044d4b7a94028c93786f8566047edc11110595914de93362559bc658"
+dependencies = [
+ "tinystr",
+]
+
 [[package]]
 name = "unicase"
 version = "2.9.0"
@@ -9370,6 +9453,7 @@ version = "0.11.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "90f911cbc359ab6af17377d242225f4d75119aec87ea711a880987b18cd7b239"
 dependencies = [
+ "serde",
  "yoke",
  "zerofrom",
  "zerovec-derive",