Allow changing source language

[Demian101]

My need is to translate Chinese mdbook files into English.
Now I have created en.po and am ready to use cloud-translate to translate it into English.

but! At this point call the cloud-translate command:

$ cloud-translate [my-project-ID] po/en.po 10000

I ran into a problem where the source_language defaulted to English and I didn't know how to change it to Chinese

---

Error info:

$ cloud-translate red-bruin-402208 po/en.po 100

Stopping translation at message 1: 邱奇-图灵（Church-Turing）
Translating 1 messages into en
Error: could not deserialize: {
  "error": {
    "code": 400,
    "message": "Target language can't be equal to source language.",
    "status": "INVALID_ARGUMENT",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.BadRequest",
        "fieldViolations": [
          {
            "field": "source_language_code",
            "description": "Source language: en_US"
          },
          {
            "field": "target_language_code",
            "description": "Target language: en"
          }
        ]
      }
    ]
  }
}


Caused by:
    missing field `translations` at line 22 column 1

grateful !

[Demian101]

Oh, i solved it by compiling it locally..

[mgeisler]

Hey @Demian101, actually... this is something we should support!

We need to make the source language here a parameter of the translate function:

cloud-translate/src/main.rs

Lines 77 to 82 in 5734aba

	let request = TranslateTextRequest {
	contents: msgids.into(),
	mime_type: "text/plain",
	source_language_code: "en_US",
	target_language_code: lang,
	};

and then somehow pass in this parameter.