Add German language support via espeak-ng (lang_code 'de') — addresses #290

[chiddekel]

German language support via espeak-ng (lang_code='de' / 'd')

Closes the practical gap behind #290: Kokoro had no German entry in its language table, even though it already drives Spanish, French, Italian, Portuguese and Hindi through espeak.EspeakG2P, and espeak-ng ships German out of the box. German just needed to join that family.

This is the pragmatic path @kneo described in #290 — "provided the correct phonemes, existing models may just work": espeak-ng produces correct German IPA, and the multilingual checkpoint consumes IPA.

Change (3 lines, no new dependency)

ALIASES   += {'de': 'd'}
LANG_CODES += {'d': 'de'}   # under the espeak-ng group
languages += ['d']          # CLI

The existing else branch then constructs EspeakG2P(language='de') automatically — no new code branch. espeak-ng is already required (it backs the English G2P fallback and every other espeak language), so there is nothing new to install.

Usage

from kokoro import KPipeline
pipe = KPipeline(lang_code='de')   # 'd' also works

python3 -m kokoro -l d --text "Guten Tag, wie geht es dir?"

Verified

"Guten Tag, wie geht es dir? Künstliche Intelligenz ist faszinierend."
→ ɡˈuːtən tˈɑːk, viː ɡˈeːt ɛs dˈiːɾ? kˈynstlɪçə ˌɪntəlɪɡˈɛnʦ ɪst fˌasʦiːnˈiːrənt.

Relationship to #317

#317 routes German to from misaki import de; de.DEG2P(), but misaki[de] does not exist on PyPI, so that path raises ImportError for every user today. This PR uses the already-working espeak path instead, so German works immediately.

Scope (honest)

Same tier and caveats as the other espeak languages: chunking isn't implemented for non-English (split long text on \n), and prosody quality varies because the base checkpoint wasn't fine-tuned on German. This is a working out-of-the-box German path now, complementary to a future dedicated misaki[de] / German fine-tune (the larger goal the #290 bounty funds).

Addresses #290