The Proceedings were, as Liebknecht explains in his preface, assembled from a mass of material, mainly in French, but also in German and English. Guesde had produced a nearly complete edited manuscript in French of this material, but this has never been published. Guesde did publish a preliminary version in French, but that only included the delegate lists and the final versions of the resolutions passed.
Much but not all of the raw material is available from the IISG Guesde archive, handwritten, but mostly digitized, and with very varying degrees of legibility. The one completely missing section is for the final Saturday session, with the crucial votes on the resolutions. Liebknecht's Proceedings seem to be a straightforward translation (with occasional minor edits) of the French edited manuscript up to that final session. For the final session the Proceedings use a newspaper report from the Berliner Volksblatt, written at the time. This is mostly used verbatim, though some details are omitted and there are minor edits in some speeches (in particular, Liebknecht seems to have felt free to make small changes to his own speeches throughout). The Volksblatt does not have the final version of the resolutions, for which Liebknecht used a version very similar to that printed by Guesde in French.
The published proceedings are therefore the end product of a series of translations and edits from multiple languages. The meaning sometimes drifts slightly from the original just because of this process, and the terminology used is not always completely consistent throughout the document. In principle it is sometimes possible to work back to a 'correct' version of the material: for example, Nieuwenhuis, Morris, Lenz and others submitted their own versions of their speeches which have survived in the archives. This has not been done: the MIA translation is a translation of the German Proceedings as published, and the original source materials have only been used occasionally to clarify ambiguous wording.
English has the pair of words 'work' and 'labour', where German uses only arbeit. I have used labour where the original refers to the abstract concept in Marxist theory (as in labour-power), or to legal aspects of work (Arbeiterschutzgesetzgebung as labour protection legislation. In references to workers as a class, I have used work, so that Arbeiterbewegung is translated as workers’ movement, where it could equally be labour movement. Similarly the various Arbeiter-Partei of different countries have been translated as 'Workers’ Party' rather than 'Labour Party'. The main reason for this is that the later division between a reformist labour movement and revolutionary socialism was beginning to emerge at this Congress, but there is no implication in the text that the Arbeiterbewegung is by nature aligned with either camp; in fact the opposite holds - most of the parties involved were trying hard to hold the two camps together.
A secondary overlapping problem is due to grammatical gender. The Congress itself was titled in German der International Arbeiter-Congress. English translations of this title at the time used the International Working-mens Congress, echoing the name of the 1st International, the International Workingmens Association. I have not followed this usage. In uses of the word arbeiter where the word is ambiguously either male or non-gendered, I have used the non-gendered but slightly anachronistic term 'worker', not 'workingman'. The exceptions are in Zetkin and Ihre's discussions of female labour, where the distinction between Arbeiter and Arbeiterin is explicit.
Another kind of problem comes from the different forms of labour organization at the time, which did not simply match across borders. A major form of organized labour in France was the Chambre Syndicale. In the proceedings, this is sometimes translated as SyndikatsKammer, sometimes as arbeitsverein. The English equivalents might be Trades Council (which is not quite the same thing: a CPGB document of 1922 defines a Chambre Syndicale as 'central committee of unions covering a single trade', though they do seem to have been local rather than national) and trades society (the translation used at the time by Bernstein). I have preferred to leave the original Chambre Syndicale where this or a strict synonym is present in the text, and the more neutral trades society where the original term is unclear. Similarly for the word Fachverein, which is generally - but not always - a translation for the word 'syndicat' in French. The German avoids the word 'union' as too tied to the English system. I have used 'professional association' or 'trade association' for 'fachverein'.
One of the main concerns of the Congress was the unity of the movement. The German Einigung is used a lot in the text, but can either mean unification or an agreement. It is used in both senses in the text, but it is not always clear which is meant. I have varied the two words as I thought appropriate to the context.
Finally, there is a lot of emphasis from the Marxist side on workers being aware of their own position. The French text generally has 'conscient', the German 'bewusste'. I have translated these as 'aware' or 'conscious' ('class-consciousness' is a separate expression, and one which only occurs a few times in the Proceedings). These terms were not enough for the German party, which wanted some way to refer to workers aware not only that they were oppressed, but that they would one day be in charge of the means of production. This is the 'zielbewusste proletariat', a phrase which occurs many times in the document; literally 'goal-conscious proletariat'. This sounds so strange in English that I have generally used 'revolutionary proletariat' though it does not have any necessary connotations of barricades in the streets.