I'm trying to translate the rules for this game - it's Viking but it's very similar to the Scottish game Ard-Rí.

One player has 1 green counter (the King) and 8 blue counters (the King's Men). The other player has 16 red counters (the Enemy).

Tá aon imreoir amháin aon licín glas amháin aige (an Rí) agus (tá sé ?) ocht licíní ghorma aige (lucht an Rí).
Tá an imreoir eile sé licíní dheirge déag aige (an Namhaid).

Open to correction or modification -

Tá licín amháin uaine ag duine dona imreoirí (an Rí)
Tá licíní ghorma ag ochtar (Fir an Rí).
Tá licíní dheirge ag an séisúr déag eile dona imreoirí (An Namhaid)

I never heard the word "licín", I would be inclined to use "cnaipe".

Go raibh maith agat

Here's the next line - I'm not at all sure how to say this in Irish:

Object (cuspóir ?): For the King's force, to move the King on to one of the 4 corner squares; for the Enemy, to trap the King.

There could be many correct ways to say this so wait for more suggestions.

Cuspóirí:
Don Rí: Bealach a réiteach don Rí go dtí ceann dona ceithre coirnéil.
Don Namhaid: An Rí a sháinniú.

Encore merci. Voici la suite:

To Play: The King is placed in the centre of the board, surrounded by his 8 men. The Enemy are placed on the 4 lots (groups) of 4 squares marked at the sides of the board.

there are mistakes you haven't corrected:

Tá licín amháin uaine ag duine do na himreoirí (an Rí)
Tá licíní gorma ag ochtar (Fir an Rí).
Tá licíní dearga ag an seisear déag eile do na himreoirí (An Namhaid)

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

actually I think there may be a mistake in Bríd's translation, there's no "ochtar" there, one player has 1 green counter and 8 blue counters (not 8 people).

So I'd say:

Tá cnaipe uaine/glas amháin (an Rí) agus ocht gcnaipe ghorma (Fir an Rí) ag imreoir amháin.
Tá sé chnaipe dhéag (an Namhaid) ag an imreoir eile.

There are only 2 players, right ?

_________________
Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

Oui c'est bien ça - d'ailleurs je ne comprenais pas bien ce qu'elle avait mis - je croyais que c'était encore moi qui avais foiré - m'enfin j'ai vu en fait que l'on peut utiliser les nombres normalement réservés aux personnes pour les choses si on ne les nomme pas. Je ne le savais pas. L'Ennemi dispose de 16 jetons rouges, pas 10.
Voici la suite -

All moves are made 1 square at a time, up or down or sideways (never diagonally).
The King's force has first move.