feat: add translation API (#297)

* feat: add translation

* feat: resurface translation by Google Translation

* feat: renamed the service as `translate` to make more readable

* fix: renamed response and request name to match rpc name

* chore: delete useless blank line

* Update publicapi.json

* Update publicapi.json

* Update README.md

Co-authored-by: Asim Aslam <asim@aslam.me>

translate/proto/translate.proto

@@ -0,0 +1,41 @@
+syntax = "proto3";
+
+package translate;
+
+option go_package = "./proto;translate";
+
+service Translate {
+  rpc Text(TextRequest) returns (TextResponse) {}
+  // TODO: implement Google Translation Advanced Edition, See https://cloud.google.com/translate/docs/advanced/translating-text-v3
+}
+
+message BasicTranslation {
+  // The translation result
+  string text = 1;
+  // The source of the query string
+  string source = 2;
+  // The model used in translation
+  string model = 3;
+}
+
+// TextRequest is the basic edition request
+message TextRequest {
+  // The contents to be translated
+  repeated string contents = 1;
+  // Source language, format in ISO-639-1 codes
+  // See https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes for more information
+  string source = 2;
+  // Target language, format in ISO-639-1 codes
+  // See https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes for more information
+  string target = 3;
+  // The string format, `text` or `html`
+  string format = 4;
+  // The model to use for translation, `nmt` or `base`,
+  // See https://cloud.google.com/translate/docs/advanced/translating-text-v3#comparing-models for more information
+  string model = 5;
+}
+
+// TextResponse is the basic edition response
+message TextResponse {
+  repeated BasicTranslation translations = 1;
+}