EN 13432 is the reference standard for industrial composting (60 °C, mixing, controlled moisture, 6 to 12 months). ISO 17556 is the standard for biodegradability in soil (ambient conditions, uncontrolled). PLA typically meets EN 13432 but not ISO 17556: it composts in an industrial facility, not in the garden or open ground. Neither of the 2 standards entitles a claim in France: "compostable" is prohibited there on plastic that composts only in an industrial facility, and "biodegradable" on any product or packaging (Article L. 541-9-1 of the Environmental Code).
Read the source article: How do you eco-design with bioplastics?