wikipedia engine builds invalid URL for region="wt-wt" (wt.wikipedia.org does not exist) #417

Before you open an issue:

• I have the latest version. (Check: ddgs version. Update: pip install -U ddgs)
• I tried reinstalling the library. (pip install -I ddgs)
• I tried using a proxy

Describe the bug

When backend="auto" is used and the wikipedia engine is selected, it constructs an invalid Wikipedia URL for the region="wt-wt" (worldwide, no regional bias) parameter. This causes a ConnectionError on every search because https://wt.wikipedia.org does not exist.

Root cause — ddgs/engines/wikipedia.py, build_payload, line 35:

_country, lang = region.lower().split("-")

For region="wt-wt" (DuckDuckGo's "no region" sentinel), this produces lang = "wt", which is not a valid ISO 639 language code. The engine then builds:

https://wt.wikipedia.org/w/api.php?action=opensearch&...

That domain does not exist, causing every call with backend="auto" to fail when the wikipedia engine is chosen.

Steps to reproduce the problem:

from ddgs import DDGS

results = DDGS().text(
    "python programming",
    region="wt-wt",   # worldwide, no regional bias
    safesearch="off",
    backend="auto",   # picks wikipedia engine
    max_results=5,
)

Expected: results returned from a working backend
Actual: ConnectionError — cannot connect to https://wt.wikipedia.org

Suggested fix: In wikipedia.py → build_payload, fall back to "en" when lang is not a recognised Wikipedia language code:

_country, lang = region.lower().split("-")
if lang == "wt" or len(lang) > 3:   # wt-wt is DDG's "worldwide" sentinel
    lang = "en"

Workaround (current): Pin backend="duckduckgo" explicitly to skip the wikipedia engine entirely.

Specify this information

• OS: Ubuntu 24.04.4 LTS on WSL2 (Linux 5.15.167.4-microsoft-standard-WSL2)
• Environment: Python 3.12.3, virtualenv
• ddgs version: 9.10.0