Description:

Added documentation to support language codes on WU

### sensor in Czech
sensor:
  - platform: wunderground
    api_key: !secret wu_key
    pws_id: KNCHOLLY21
    lang: CZ
    monitored_conditions:
      - alerts
      - weather
      - temp_c

### sensor in Brazilian portuguese
sensor:
  - platform: wunderground
    api_key: !secret wu_key
    pws_id: KNCHOLLY21
    lang: BR
    monitored_conditions:
      - alerts
      - weather
      - temp_c

### sensor in French
sensor:
  - platform: wunderground
    api_key: !secret wu_key
    pws_id: KNCHOLLY21
    lang: FR
    monitored_conditions:
      - alerts
      - weather
      - temp_c

Supported Language Codes

AF Afrikaans
AL Albanian
AR Arabic
HY Armenian
AZ Azerbaijani
EU Basque
BY Belarusian
BU Bulgarian
LI British English
MY Burmese
CA Catalan
CN Chinese - Simplified
TW Chinese - Traditional
CR Croatian
CZ Czech
DK Danish
DV Dhivehi
NL Dutch
EN English
EO Esperanto
ET Estonian
FA Farsi
FI Finnish
FR French
FC French Canadian
GZ Galician
DL German
KA Georgian
GR Greek
GU Gujarati
HT Haitian Creole
IL Hebrew
HI Hindi
HU Hungarian
IS Icelandic
IO Ido
ID Indonesian
IR Irish Gaelic
IT Italian
JP Japanese
JW Javanese
KM Khmer
KR Korean
KU Kurdish
LA Latin
LV Latvian
LT Lithuanian
ND Low German
MK Macedonian
MT Maltese
GM Mandinka
MI Maori
MR Marathi
MN Mongolian
NO Norwegian
OC Occitan
PS Pashto
GN Plautdietsch
PL Polish
BR Portuguese
PA Punjabi
RO Romanian
RU Russian
SR Serbian
SK Slovak
SL Slovenian
SP Spanish
SI Swahili
SW Swedish
CH Swiss
TL Tagalog
TT Tatarish
TH Thai
TR Turkish
TK Turkmen
UA Ukrainian
UZ Uzbek
VU Vietnamese
CY Welsh
SN Wolof
JI Yiddish - transliterated
YI Yiddish - unicode

All supported languages are listed at https://www.wunderground.com/weather/api/d/docs?d=language-support&MR=1

Pull request in home-assistant (if applicable): home-assistant/core#4815