@Anand Tp Unfortunately, this isn't a valid language pair that is supported for dictionary lookup API. English is the only pair that is supported for French for this API. You can check the supported languages for translation, transliteration and dictionary using the languages API to get the complete list and then use the supported languages.
"fr": {
"name": "French",
"nativeName": "Français",
"dir": "ltr",
"translations": [
{
"name": "English",
"nativeName": "English",
"dir": "ltr",
"code": "en"
}
]
}
A workaround for your scenario is to use the lookup API for FR-EN and then EN-DE.