feat: Add types for i18n module of cds 8.5.

apis/facade.d.ts

@@ -7,6 +7,7 @@ export * from './events'
 export * from './utils'
 export * from './cqn'
 export * from './global'
+export * from './i18n'
 export { log, debug } from './log'
 export { test } from './test'
 

apis/i18n.d.ts

@@ -0,0 +1,46 @@
+import { csn, entity } from './cds'
+
+
+declare class I18nBundle {
+  constructor(options: I18nFilesOptions)
+  for(key: number | string | object, locale?: string | object, args?: object): string | undefined
+  at(key: number | string | object, locale?: string | object, args?: object): string | undefined
+  file: string
+  files: I18nFiles
+  get defaults(): Record<string, string>
+  get fallback(): Record<string, string>
+  key4(definition: entity): string
+  texts4 (locale: string): Texts
+  translations4 (...locales : 'all' | string[]) : { [locale]: Texts }
+}
+
+declare class I18nFacade {
+  Bundle: typeof I18nBundle
+  Facade: typeof I18nFacade
+  Files: typeof I18nFiles
+  get file(): string
+  get folders(): string[]
+  get labels(): I18nBundle
+  get messages(): I18nBundle
+
+  bundle4 (file: string, options?: I18nFilesOptions): I18nBundle
+  bundle4 (model: csn.CSN): I18nBundle
+
+}
+
+interface I18nFilesOptions {
+  file?    : string   
+  model?   : csn.CSN     
+  roots?   : string[] 
+  leafs?   : string[] 
+  folders? : string[]
+}
+
+declare class I18nFiles {
+  constructor (options: I18nFilesOptions)
+  get options(): I18nFilesOptions
+  get basename(): string
+  content4(locale: string, suffix: string): Array<object>
+}
+
+export declare const i18n: I18nFacade

test/typescript/apis/project/cds-i18n.ts

@@ -0,0 +1,35 @@
+import cds, { i18n } from "@sap/cds";
+import { testType } from "./dummy";
+const model = cds.reflect({});
+const { Book: Books } = model.entities;
+
+testType<string | undefined>(i18n.labels.for("foo"));
+testType<string | undefined>(i18n.labels.at("foo"));
+i18n.labels.at("foo", "bar");
+i18n.labels.at("foo", "bar", [123, "baz"]);
+i18n.labels.at("foo", [123, "baz"]);
+i18n.labels.file = "";
+// @ts-expect-error
+i18n.labels.defaults = {
+  foo: "bar",
+};
+// @ts-expect-error
+i18n.labels.fallback = {
+  foo: "bar",
+};
+
+testType<string | undefined>(i18n.messages.for("foo"));
+testType<string | undefined>(i18n.messages.at("foo"));
+i18n.messages.at("foo", "bar");
+i18n.messages.at("foo", "bar", [123, "baz"]);
+i18n.messages.at("foo", [123, "baz"]);
+
+i18n.bundle4("foo", { file: "bar" });
+i18n.labels.texts4("de");
+i18n.labels.translations4("de");
+i18n.labels.key4(Books);
+i18n.messages.texts4("de");
+i18n.messages.translations4("de");
+i18n.messages.key4(Books);
+cds.i18n.labels.for("foo");
+cds.i18n === i18n;