You are welcome to try your hand at translating. I've got a bunch of these and I'm planning to make translations public available (giving them away) because the source documents are often bound by copyright restrictions.
1 Cest endenture faite parentre Johan filz du roi Dengleterre, duc de Lancastre, dune part, et mons[ire] Johan de Ipres, dautre part, tesmoigne qe le dit mons[ire] Johan est demorez envers le dit duc' pur peas et pur guerre a terme de vie.
2 Por quele demeore ensemblement et pur le bon et greable service qil ad fait au dit duc' es parties Despaigne et aillours, et me[sme]ment por le mielz meintenir lordre de chivaler qil prist de lui le jour de la bataille de Nazare, le dit duc ad donez et grantez au dit mons[ire] Johan vint livres dargent par an a terme de sa vie a prendre dan en an des issues des villes de Overton et Slyne deinz le wapentak de Lonnesdale en le duchee de Lancastre par les meins des provostz illeoqes qore sont ou qe pur le temps serront a les termes illeoqes usueles par oveles porcions, cest assavoir x li. de la dite ville de Overton' et autres x li. de la dite ville de Slyne.
3 Et le dit duc' voet et grante pur lui et pur ses heirs qe, si la dite annuite de xx li. soit aderer par deux mois en partie ou en tout as nulles des dites termes, qe bien lise a dit mons[ire] Johan de Ipres entrere les dites villes et illeoqes destreindre et les destreces enchater et detenir tanque gree lui ent soit fait des arrerages lui ent duez.
4 En tesmoignance de queu chose les avantditz duc en mon dit s[ire] Johan a les parties de cestes endentures entrechangeablement on mis lour sealx.
5 Don' a chastel de Hertford' le viij jour de decembre, lan du regne nostre dit seignur le roi quarante primere.
My very rough translation:
1 This indenture made between John son of the king of England, duke of Lancaster, on one part, and sir John de Ypres, on the other part, testifies that the said Sir John is bound(?) to the said duke for peace and for war for a life term.
2 [The first part of this unclear to me. Too many unfamiliar words. But it appears that John of Ypres served the Duke at the Battle of Najera and in consideration of this and his future service is being granted an annual income of twenty silver livres. This income is to be drawn on the revenues of the villages Overton and Slyne in the wapentak(???) of Lnnesdale in the duchy of Lancaster. The income shall be equally divided, 10 livres from Overton, 10 livres from Slyne.]
3 [Grants the right of distraint to Sir John, or his heirs, if the annuity is two months overdue.]
4 In testimony of which the aforesaid duke and Sir John, who are the parties of this indenture, attach their seals.
5 Done at the castle of Hertford on the 8th day of december, in the 40th year of the reign of our lord the king.