That is not entirely true, for linguists know too much about language to suggest that there ever was, literally, a single language from which all Indo-European languages descended.
( That ( ( ( ( ( is not ) ( entirely true ) ) , ) ( for ( linguists ( ( know ( ( too much ) ( about language ) ) ) ( to ( suggest ( that ( there ( ever ( ( ( ( was , ) literally ) , ) ( ( a ( single language ) ) ( ( from which ) ( ( all ( Indo-European languages ) ) descended ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT That)) (VP (VBZ is) (RB not) (ADJP (RB entirely) (JJ true)) (, ,) (SBAR (IN for) (S (NP (NNS linguists)) (VP (VBP know) (ADVP (ADVP (RB too) (RB much)) (PP (IN about) (NP (NN language)))) (S (VP (TO to) (VP (VB suggest) (SBAR (IN that) (S (NP (EX there)) (ADVP (RB ever)) (VP (VBD was) (, ,) (ADVP (RB literally)) (, ,) (NP (NP (DT a) (JJ single) (NN language)) (SBAR (WHPP (IN from) (WHNP (WDT which))) (S (NP (DT all) (JJ Indo-European) (NNS languages)) (VP (VBD descended))))))))))))))) (. .)))
The one language from which all Indo-European languages descended will be announced soon.
( ( ( The ( one language ) ) ( ( from which ) ( ( all ( Indo-European languages ) ) descended ) ) ) ( ( will ( be ( announced soon ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (CD one) (NN language)) (SBAR (WHPP (IN from) (WHNP (WDT which))) (S (NP (DT all) (JJ Indo-European) (NNS languages)) (VP (VBD descended))))) (VP (MD will) (VP (VB be) (VP (VBN announced) (ADVP (RB soon))))) (. .)))