Systems and methods are provided for training and using a novel unified language foundation model. An encoder-decoder natural language model is obtained and various training data is obtained and used for training. The training process integrates a combination of replaced token detection, corrupted span reconstruction, and disentangled attention methodologies to produce a unified encoder-decoder model. The trained model is trained for performing both natural language understanding (NLU) tasks and natural language generation (NLG) tasks. Attention applied to the model is applied discretely to segmented chunks of encoded data during processing to improve the efficiency of applying attention by the model.