Adding a description to the usage rates isn't a bad idea, but we should keep the structure of usage rates otherwise consistent with the current API:
```
{
    "plan_id": "plan1",
    "brl": 0.01,
    "cad": 0.02,
    "eur": 0.03,
    "usd": 0.04,
    "duration": "hour",
    "description": "This gear costs an additional %{currency}%{rate} per gear-%{duration} after the first 3 gears."
},
{
    "plan_id": "plan2",
    "brl": 0.10,
    "cad": 0.20,
    "eur": 0.30,
    "usd": 0.40,
    "duration": "hour"
    "description": "This gear costs an additional %{currency}%{rate} per gear-%{duration} after the first 3 gears."
}
```

Translation is something we will probably handle API-wide in the future via an accept-language header rather than pushing all translations for all messages to all clients