I have tried to translate the sentence into English.
The original German is:
Die Sprache ist gleichsam die äußerliche Erscheinung des Geistes* der Völker**; ihre Sprache ist ihr Geist und ihr Geist ihre Sprache; man kann sich beide nie identisch genug denken.
* single, genetive.
** plural, genetive.
"Goolge translate" trnaslated the sentence into English as the following:
The language is, so to speak, the external manifestation of the spirit of the people; their language is their mind and their mind their language; one can never imagine the two identical enough.
I have tried to translate the sentence into:
The language is, as it were, the appearance of the mind of the people. Their language is their mind and their mind is their language; people could never imagine enough that two languages are identical.
"Geist" is translated into “mind”.
"die äußerliche Erscheinung” could be translated into “appearance” in p. 1322 In Harper Collins German Unabridged Dictionary.
"ihre Sprache ist ihr Geist und ihr Geist ihre Sprache" is translated into “Their language is their mind and their mind is their language".
Hope people who know German could correct my translation and people who use English could correct my English.
Thank you.
