The Holy Prophet(sa) taught a particular way to perform Istikhara and that should be adopted. However, the spirit of Istikhara, as the name suggests, is to pray before Allah and seek his blessings in a particular task, therefore if someone has not memorised the exact Arabic prayer for Istikhara there is no harm for them to read its translation – or a similar prayer – in whatever language they liked.
The preferred way however is to offer Istikhara in the manner the Holy Prophet(sa) taught.