Helping a friend review quotes, both said "supports multiple languages," but the prices differed by three times. He wasn't convinced and felt the more expensive one was ripping people off. After breaking down the quote structure, he changed his tune.
The cheaper solution uses a file-based language pack, where translation only covers interface copy, and adding a language means adding a translation file. The more expensive solution uses a database-based approach plus a translation workflow, where operational content can also be multilingual, with translation status, terminology management, and version comparison all included. The former is "interface multilingual," while the latter is "business multilingual"—they are not the same thing. For details on architecture selection, see the multi-language platform build topic.
Pure machine translation, machine translation plus human proofreading, and pure human translation—the cost ratio of these three workflows is roughly 1:3:8. If the quote does not specify the translation workflow, be sure to ask—this part of the price difference can account for 20% of the total quote.
Independent URL structure, hreflang configuration, and per-language meta management—only with these can multilingual traffic even be discussed. A solution that only translates the interface without changing the URL structure will have its multilingual pages seen by search engines as duplicate content.
Expensive solutions usually come with multilingual content distribution tools: publish once, synchronize across languages, and reminders for missing translations. Cheap solutions rely on manually switching between backends for maintenance. As languages increase, the speed at which labor costs overtake expectations exceeds what most people anticipate.
When you get a quote, check it item by item against these four sources: Is the architecture specified? Is the translation workflow specified? Is SEO infrastructure included? Are operations tools included? A more expensive solution that includes all four is worth it in most cases; a cheap solution that includes none of the four will have the money saved paid back in other forms. For more market observations, see the Insight & Observations section.