Notion, Backlog and Linear: compare the job, not the label
A documentation workspace, a project tracker and an engineering issue system overlap without being interchangeable. Begin with the work that currently gets lost.
Trial one real project
Use the same tasks, documents and participants in each candidate. Ask people to assign work, find a decision, record a change and close an item. Include occasional contributors as well as the people who will administer the tool.
Test the Japanese and English experience directly. Check the current plan’s permissions, integrations, exports and collaboration limits. Do not treat an old price table or a broad claim about Japanese teams as a substitute for the trial.
Keep documents and actions connected
A project may need both durable documentation and a disciplined task workflow. If you use more than one product, define which owns each record and how references stay current. Avoid maintaining the same task manually in two places.
Budget for administration and training as well as licenses. An adaptable workspace needs somebody to maintain its structure; an opinionated tracker may need the team to change its process.
Choose from the evidence of your trial. The useful result is that staff know where to look and what to do next, not that the company has adopted the tool with the most enthusiastic following.