It is the "acts" of Vatican II (docuмents, interventions, etc.—"primarily in Latin, with some text in English, French, German, Italian, Spanish, or Arabic"). I just discovered today that a certain MHazell user on Archive.org uploaded scans of first 10 volumes of the Acta (of the pre-session and sessions 1 and 2) within the past few years! Deo gratias!

From here, this is the layout of the Acta volumes:

V. 1. Periodus Prima. Pars 1: Sessio Publica I. Congregationes Generales I-IX. --
v. 1. Pars 2: Congregationes Generales X-XVIII. --
v. 1. Pars 3: Congregationes Generales XIX-XXX. --
v. 1. Pars 4: Congregationes Generales XXXI-XXXVI. --
v. 2. Periodus Secunda. Pars 1: Sessio Publica II. Congregationes Generales XXXVII-XXXIX. --
v. 2. Pars 2: Congregationes Generales XL-XLIX. --
v. 2. Pars 3: Congregationes Generales L-LVIII. --
v. 2. Pars 4: Congregationes Generales LIX-LXIV. --
v. 2. Pars 5: Congregationes Generales LXV-LXXII. --
v. 2. Pars 6: Congregationes Generales LXXIV-LXXIX. Sessio Publica III. --
v. 3. Periodus Tertia. Pars 1: Sessio Publica IV. Congregatines Generales LXXX-LXXXII. --
v. 3. Pars 2: Congregationes Generales LXXXIII-LXXIX. --
v. 3. Pars 3: Congregationes Generales XC-XCV. --
v. 3. Pars 4: Congregationes Generales XCVI-CII. --
v. 3. Pars 5: Congregationes Generales CII-CXI. --
v. 3. Pars 6: Congregationes Generales CXII-CXVIII. --
v. 3. Pars 7: Congregationes Generales CXIX-CXXII. --
v. 3. Pars 8: Congreationes generales CXXIII-CXXVII. Sessio Publica V. --
v. 4. Periodus Quarta. Pars 1: Sessio Publica VI. Congregationes Generales CXXVIII-CXXXII. --
v. 4. Pars 2: Congregationes Generales CXXXIII-CXXXVII. --
v. 4. Pars 3: Congregationes Generales CXXXVIII-CXLV. --
v. 4. Pars 4: Congregationes Generales CXLVI-CL. --
v. 4. Pars 5: Congretiones Generales CLI-CLV. Sessio Publica VII. --
v. 4. Pars 6: Congregationes Generales CLVI-CLXIV. Sessio Publica VIII. --
v. 4. Pars 7: Congregationes Generales CLXV-CLXVIII. Sessiones Publicae IX-X. --
[v. 5.]. Indices. [1980]. --
[v. 6.]. Appendix. [1983].

Maybe this will inspire some generous soul to scan the 16 other volumes!

Deo gratias!

P.S. — There are translations of the first sessions' schemas in Fr. komonchak's free "The Council That Might Have Been"