[WIP][examples/seq2seq] move old s2s scripts to legacy (#10136)

* move old s2s scripts to legacy

* add the tests back

* proper rename

* restore

* Apply suggestions from code review

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

Co-authored-by: Stas Bekman <stas@stason.org>
Co-authored-by: Stas Bekman <stas00@users.noreply.github.com>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

examples/legacy/seq2seq/test_data/fsmt/build-eval-data.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python
+
+import io
+import json
+import subprocess
+
+
+pairs = [
+    ["en", "ru"],
+    ["ru", "en"],
+    ["en", "de"],
+    ["de", "en"],
+]
+
+n_objs = 8
+
+
+def get_all_data(pairs, n_objs):
+    text = {}
+    for src, tgt in pairs:
+        pair = f"{src}-{tgt}"
+        cmd = f"sacrebleu -t wmt19 -l {pair} --echo src".split()
+        src_lines = subprocess.run(cmd, stdout=subprocess.PIPE).stdout.decode("utf-8").splitlines()
+        cmd = f"sacrebleu -t wmt19 -l {pair} --echo ref".split()
+        tgt_lines = subprocess.run(cmd, stdout=subprocess.PIPE).stdout.decode("utf-8").splitlines()
+        text[pair] = {"src": src_lines[:n_objs], "tgt": tgt_lines[:n_objs]}
+    return text
+
+
+text = get_all_data(pairs, n_objs)
+filename = "./fsmt_val_data.json"
+with io.open(filename, "w", encoding="utf-8") as f:
+    bleu_data = json.dump(text, f, indent=2, ensure_ascii=False)